Set `$VIRTUALENV_DIRS` for `$CLEAN_VIRTUALENV`
Set `$VIRTUALENV_DIRS` for `$CLEAN_VIRTUALENV`

I had to do this to wipe out my virtualenv -- there may be a more appropriate solution.
Nazanin84/python-buildpack,ywarezk/heroku-buildpack-geodjango,Gliimpse/heroku-buildpack-SWIG-python,kikin81/heroku-buildpack,stalnacke/heroku-buildpack-python,craigkerstiens/gistlog,pwdel1/heroku-buildpack-scipy,cortexintel/heroku-buildpack-scipy,jimlindeman/python-buildpack-collectd,rawWhipIT/p22-goldant-buildpack,benmurden/heroku-buildpack-python-ember,drinks/heroku-buildpack-python-scipy,samuelhavron/heroku-buildpack-python,dbrgn/heroku-npscipy,maxcountryman/heroku-buildpack-python,cloudControl/buildpack-python,marcospy/hackathon-globo-app,markine/heroku-buildpack-python,ianyh/heroku-buildpack-python-extras,beni55/heroku-buildpack-python,osharim/-heroku-buildpack-python,lukaszkorecki/heroku-buildpack-python,nicktimko/heroku-buildpack-scipy,gitricko/apt-python-buildpack,buildbot/buildbot-master-buildpack,grivescorbett/heroku-buildpack-python,ruscoder/heroku-buildpack-python,Nazanin84/python-buildpack,liyanchang/cloudfoundary-buildbot-buildpack,samuelhavron/heroku-buildpack-python,orablu/heroku-buildpack,Brogency/heroku-buildpack-python-gulp,mythmon/heroku-buildpack-python-nodejs,alexluke/heroku-buildpack-python-extras,andrespires/python-buildpack,tukutela/heroku-buildpack-python,YoApp/heroku-buildpack-python-twemproxy,rawWhipIT/p22-goldant-buildpack,buildingenergy/heroku-buildpack-python-leatherman,liyanchang/cloudfoundary-buildbot-buildpack,mfenniak/heroku-buildpack-python-libffi,aldryn/heroku-buildpack-python,apiaryio/heroku-buildpack-python-scons,jbenet/heroku-buildpack-python,localmed/heroku-buildpack-python-extras,brianthomas/heroku-buildpack-textmining,cloudfoundry/python-buildpack,rbtying/heroku-buildpack-python,miraculixx/heroku-buildpack-python,jbenet/heroku-buildpack-python,jms6520/cf-python,heroku/heroku-buildpack-python,orablu/heroku-buildpack,kvarga/heroku-buildpack-python,jimlindeman/python-buildpack-collectd,sookasa/heroku-buildpack-python-pipeline,integricho/heroku-buildpack-python-ffmpeg-lame,predata/heroku-buildpack-scipy,scrapinghub/scrapinghub-buildpack-scrapy,osharim/-heroku-buildpack-python,Scalingo/python-buildpack,kikin81/heroku-buildpack,rajpurkar/heroku-buildpack-python-sklearn,18F/python-buildpack,dulaccc/heroku-buildpack-geodjango,julienbou/heroku-buildpack-serpan,ephemerallabs/heroku-buildpack-python,legnaleurc/heroku-buildpack-python,pkumar-appd/python-buildpack,benjaminfox/heroku-buildpack-python-geoip,Gliimpse/heroku-buildpack-SWIG-python,samuelhavron/heroku-buildpack-python,SciDevs/heroku-buildpack-python-scikit-learn-git,blazekadam/open2,integricho/heroku-buildpack-python-ffmpeg-lame,legnaleurc/heroku-buildpack-python,psrthegreat/heroku-buildpack-python-sklearn,edmorley/heroku-buildpack-python,rapilabs/heroku-buildpack-python,liyanchang/cloudfoundary-buildbot-buildpack,Apogaea/heroku-buildpack-python,davidcbucher/heroku-buildpack-geo-python,slorg1/heroku-buildpack-python,zakdoek/heroku-buildpack-django,dbrgn/heroku-buildpack-python-sklearn,osharim/-heroku-buildpack-python,vlidholt/heroku-buildpack-scipy,drinks/heroku-buildpack-python-scipy,junyoed/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,AltSchool/heroku-buildpack-python,doda/heroku-buildpack-python,ianyh/heroku-buildpack-python-extras,cirlabs/heroku-buildpack-geodjango,buildingenergy/heroku-buildpack-python-leatherman,evnpr/herokupython,davidcbucher/heroku-buildpack-geo-python,amanjain/heroku-buildpack-python-with-django-bower,manufacturedba/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,andrespires/python-buildpack,integricho/heroku-buildpack-python-ffmpeg-lame,film42/heroku-buildpack-python-wkhtmltopdf,kowito/python-buildpack,projetoeureka/heroku-buildpack-scipy,craigkerstiens/gistlog,kennethjiang/heroku-buildpack-python-libffi,hsr-ba-fs15-dat/heroku-buildpack,Nazanin84/python-buildpack,river-jade/heroku-buildpack-scipy,craigkerstiens/gistlog,Gliimpse/heroku-buildpack-SWIG-python,Scalingo/python-buildpack,18F/python-buildpack,evnpr/herokupython,sjtuadamyang/adamyang-buildpack-python-libjpeg,nwkotto/geodjango-buildpack-with-geos,integricho/heroku-buildpack-python-ffmpeg2.1-with-codecs,cloudfoundry/python-buildpack,guidowb/buildpack-python,uniphil/heroku-buildpack-pythonsass,mfenniak/heroku-buildpack-python-libffi,craigkerstiens/gistlog,ianyh/heroku-buildpack-python-opencv,cirlabs/heroku-buildpack-geodjango,codeforamerica/heroku-buildpack-pygeo,heroku/heroku-buildpack-python,SciDevs/heroku-buildpack-python-scikit-learn-git,drinks/heroku-buildpack-python-scipy,codeforamerica/heroku-buildpack-pygeo,evnpr/herokupython,rajpurkar/heroku-buildpack-python-sklearn,aldryn/heroku-buildpack-python,thenovices/heroku-buildpack-scipy,apiaryio/heroku-buildpack-python-scons,everysignalinc/heroku-buildpack-python-scikit-learn-git,maciejgryka/heroku-buildpack-spcedge,skilljar/heroku-buildpack-python,zakdoek/heroku-buildpack-django,samuelhavron/heroku-buildpack-python,arnfred/heroku-buildpack-python-hdf5-blas-lapack,nemesiscodex/heroku-buildpack-python,drinks/heroku-buildpack-python-scipy,cloudfoundry/python-buildpack,wbrefvem/heroku-buildpack-python,tommyvn/heroku-buildpack-python,igroff/heroku-buildpack-python,doda/heroku-buildpack-python,ekkleesia2/heroku-buildpack-python,jms6520/cf-python,rollokb/heroku-buildpack-python,dubsmash/heroku-buildpack-python,benjaminfox/heroku-buildpack-python-geoip,alexflanagan/operand-buildpack-python,nadirizr/heroku-buildpack-python-gulp,arnfred/heroku-buildpack-python-hdf5-blas-lapack,davidcbucher/heroku-buildpack-geo-python,apiaryio/heroku-buildpack-python-scons,marcospy/heroku-buildpack-scipy,Stibbons/heroku-buildpack-python-installer,jamarparris/heroku-buildpack-python-swig,ryanhiebert/heroku-buildpack-python,marcospy/hackathon-globo-app,joshisa/python-buildpack,nikita-pivovarov/heroku-buildpack-python-ldap,icoxfog417/heroku-buildpack-python,ad-m/heroku-buildpack-python,monological/heroku-buildpack-python-opencv,mfenniak/heroku-buildpack-python-libffi,jms6520/cf-python,mobify/heroku-buildpack-python-swig,guidowb/buildpack-python,lyft/heroku-buildpack-python-data,liyanchang/buildbot-master-buildpack,gitricko/apt-python-buildpack,econchick/heroku-buildpack-python,gitricko/apt-python-buildpack,HanSooloo/heroku-buildpack-python,ianyh/heroku-buildpack-python-extras,julienbou/heroku-buildpack-serpan,soapril/heroku-buildpack-python,joshowen/heroku-buildpack-python,sookasa/heroku-buildpack-python-pipeline,guidowb/buildpack-python,ianyh/heroku-buildpack-python-bower,econchick/heroku-buildpack-python,lyft/heroku-buildpack-python-data,uniphil/heroku-buildpack-pythonsass,psrthegreat/heroku-buildpack-python-sklearn,uniphil/heroku-buildpack-pythonsass,Tiger66639/buildbot-master-buildpack,joshisa/python-buildpack,ianyh/heroku-buildpack-python-opencv,swils/heroku-buildpack-python,psrthegreat/heroku-buildpack-python-sklearn,benmurden/heroku-buildpack-python-ember,kennethjiang/heroku-buildpack-python-libffi,jimlindeman/python-buildpack-collectd,jbenet/heroku-buildpack-python,localmed/heroku-buildpack-python-extras,SciDevs/heroku-buildpack-python-scikit-learn-git,cclauss/heroku-buildpack-python,xica/heroku-buildpack-scipy,econchick/heroku-buildpack-python,jvenezia/heroku-buildpack-python,alexflanagan/operand-buildpack-python,PerceptumNL/heroku-buildpack-python,AltSchool/heroku-buildpack-python,brightforme/heroku-buildpack-python,agriffis/heroku-buildpack-python,dvreed/heroku-buildpack-python-ldap,18F/python-buildpack,dbrgn/heroku-buildpack-python-sklearn,evnpr/herokupython,ad-m/heroku-buildpack-python,film42/heroku-buildpack-python-wkhtmltopdf,everysignalinc/heroku-buildpack-python-scikit-learn-git,rawWhipIT/p22-goldant-buildpack,cirlabs/heroku-buildpack-geodjango,resmio/heroku-buildpack-geodjango,swanson/heroku-buildpack-python-ortools,arnfred/heroku-buildpack-python-hdf5-blas-lapack,adamroth/heroku-buildpack-python-pdftk,pmclanahan/heroku-buildpack-python-peep,oberlin/heroku-buildpack-python,dbrgn/heroku-npscipy,orablu/heroku-buildpack,pkumar-appd/python-buildpack,plangrid/heroku-buildpack-python,HousekeepLtd/heroku-buildpack-python,davidcbucher/heroku-buildpack-geo-python,ojacobson/heroku-buildpack-python,kikin81/heroku-buildpack,driftyco/heroku-buildpack-sphinx,kowito/python-buildpack,alexluke/heroku-buildpack-python-extras,marcospy/hackathon-globo-app,wbrefvem/heroku-buildpack-python,jms6520/cf-python,joshisa/python-buildpack,papaeye/heroku-buildpack-python-bower,gaumire/heroku-buildpack-python,smalleats/heroku-buildpack-python,martingascon/heroku-buildpack-python,kennethjiang/heroku-buildpack-python-libffi,econchick/heroku-buildpack-python,Mause/heroku-buildpack-python,dbrgn/heroku-npscipy,rajpurkar/heroku-buildpack-python-sklearn,WonderThink/heroku-buildpack-python-ffmpeg-geoip,everysignalinc/heroku-buildpack-python-scikit-learn-git,arnaudlimbourg/heroku-buildpack-python,localmed/heroku-buildpack-python-extras,lyft/heroku-buildpack-python-data,cdht/heroku-buildpack-python,loanzen/heroku-buildpack-python,ianyh/heroku-buildpack-python-opencv,pebble/cloudpebble-buildpack,sookasa/heroku-buildpack-python-pipeline,kowito/python-buildpack,TipWander/heroku-buildpack-geodjango,film42/heroku-buildpack-python-wkhtmltopdf,ianyh/heroku-buildpack-python-nodejs,orablu/heroku-buildpack,aldryn/heroku-buildpack-python,kikin81/heroku-buildpack,joshfriend/heroku-buildpack-python,edenspiekermann-amsterdam/heroku-buildpack-python,ianyh/heroku-buildpack-python-nodejs,pkumar-appd/python-buildpack,andela-brotich/wger-buildpack-python,marianzange/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,RobertSundling/heroku-buildpack-python-nginx,ianyh/heroku-buildpack-python-nodejs,samuelhavron/heroku-buildpack-python,DylanLukes/heroku-buildpack-python,bobsilverberg/heroku-buildpack-python-peep,andrespires/python-buildpack,buildingenergy/heroku-buildpack-python-leatherman,tukutela/heroku-buildpack-python,jbenet/heroku-buildpack-python,legnaleurc/heroku-buildpack-python,dbrgn/heroku-buildpack-python-sklearn