do not override custom excerpt set in YAML frontmatter
do not override custom excerpt set in YAML frontmatter

Fixes #933.

m2candre/jekyll,dezon/jekyll,AnanthaRajuC/jekyll,kuangyeheng/jekyll,tareq-s/jekyll,hiteshsuthar/jekyll,princeofdarkness76/jekyll,jeffkole/jekyll,ramoslin02/jekyll,rlugojr/jekyll,rongl/jekyll,ajhit406/jekyll,stomar/jekyll,backendeveloper/jekyll,codeclimate-testing/jekyll,cyberid41/jekyll,nasht00/jekyll,alihalabyah/jekyll,xtymichael/jekyll,mixxmac/jekyll,cyberid41/jekyll,Teino1978-Corp/jekyll,wadaries/jekyll,derekgottlieb/jekyll,zhangkuaiji/jekyllcn,ryanshaw/jekyll,chrisfinazzo/jekyll,leichunxin/jekyll,oresmus/jekyll,fulldecent/jekyll,sanxore/sanxore.github.com,zsyed91/jekyll,ajhit406/jekyll,zsyed91/jekyll,greent2008/jekyll,monxim/monxim.github.io,krishnakalyan3/jekyll,egobrightan/jekyll,rovrevik/jekyll,UniFreak/jekyllcn,alex-kovac/jekyll,pheuko/jekyll,likong/jekyll,abhilashhb/jekyll,FlyingWHR/jekyll,jmhardison/jekyll,digideskio/jekyll,drobati/jekyll,alex-kovac/jekyll,kuangyeheng/jekyll,0x00evil/jekyll,greent2008/jekyll,anthonyrosengren/grasshoppergathering2.github-io,sanxore/sanxore.github.com,CPVPLachlan/CPVP-Blog,darwin/jekyll,hubsaysnuaa/jekyll,matuzo/jekyll,naughtyboy83/jekyll,naughtyboy83/jekyll,xiongjungit/jekyll,brint/jekyll,omeripek/jekyll,Kinghack/kinghack.github.com,supriyantomaftuh/jekyll,egobrightan/jekyll,tomjohnson1492/jekyll,yihangho/jekyll,bsmr-ruby/jekyll,winndows/jekyll,Kinghack/kinghack.github.com,getandpost/jekyll.github.io,Strangehill/jekyll,xcatliu/jekyllcn,codeclimate-testing/jekyll,chrisfinazzo/jekyll,EddieDow/jekyll,wentixiaogege/jekyll,superve/jekyll,trungvothanh/jekyll,kimeng/jekyll,lcustodio/lcustodio.github.io_base,AtekiRyu/jekyll,schaazzz/jekyll,Tyrion22/jekyll,iRoxx/jekyll,julienbourdeau/jekyll,pmarsceill/jekyll,nickg33/jekyll,MjAbuz/jekyll,daniel-beck/jekyll,nateberkopec/jekyll,brint/jekyll,royalwang/jekyll,yihangho/jekyll,chrisfinazzo/jekyll,tillgrallert/jekyll,wentixiaogege/jekyll,chiyodad/jekyll,PepSalehi/jekyll,howkj1/jekyll,MauroMrod/jekyll,royalwang/jekyll,egobrightan/jekyll,gencer/jekyll,stevecrozz/jekyll,isathish/jekyll,gynter/jekyll,leichunxin/jekyll,alex-kovac/jekyll,PepSalehi/jekyll,stevecrozz/jekyll,tylermachen/jekyll,nfagerlund/jekyll,stomar/jekyll,jmknoll/jekyll,jekyll/jekyll,zhangkuaiji/jekyllcn,vcgato29/jekyll,eninya/jekyll,hartmel/jekyll,chiyodad/jekyll,cyberid41/jekyll,harrissoerja/jekyll,penchan1218/jekyllcn,jekyll/jekyll,imaustink/jekyll,pmarsceill/jekyll,pheuko/jekyll,pmarsceill/jekyll,CheekyFE/jekyll,sferik/jekyll,angeliaz/jekyll,akoeplinger/jekyll,fulldecent/jekyll,nasht00/jekyll,shuber2/jekyll,ducktyper/jekyll,eninya/jekyll,gynter/jekyll,CheekyFE/jekyll,AtekiRyu/jekyll,mrb/jekyll,garvitr/jekyll,LuoPX-15510486969/jekyll,thejameskyle/jekyll,1gitGrey/jekyll,xcatliu/jekyllcn,nasht00/jekyll,tomjohnson1492/jekyll,nemotan/jekyll,mrb/jekyll,ramoslin02/jekyll,krahman/jekyll,nateberkopec/jekyll,fengsmith/jekyll,18F/jekyll,nateberkopec/jekyll,lazycai/lazycai.github.com,trungvothanh/jekyll,ZainRizvi/jekyll,htmelvis/jekyll,Teino1978-Corp/Teino1978-Corp-jekyll,MauroMrod/jekyll,gencer/jekyll,digideskio/jekyll,howkj1/jekyll,xiebinhqy/jklly_china,ls2uper/jekyll,jaroot32/jekyll,QuinntyneBrown/jekyll,nasht00/jekyll,gaosboy/jekyll,tobscure/jekyll,ajhit406/jekyll,christophermanning/jekyll,dangaute/eng,rovrevik/jekyll,vidbina/jekyll,isathish/jekyll,ReachingOut/jekyll,FlyingWHR/jekyll,fengsmith/jekyllcn,fabulousu/jekyll,kinlane/jekyll,indraj/jekyll,jeffkole/jekyll,sideci-sample/sideci-sample-jekyll,bsmr-ruby/jekyll,xiaoshaozi52/jekyll,codeclimate-testing/jekyll,rajrathore/jekyll,oresmus/jekyll,hubsaysnuaa/jekyll,rongl/jekyll,emarchak/tomes-jekyll,drobati/jekyll,alfredxing/jekyll,jmhardison/jekyll,winndows/jekyll,Teino1978-Corp/jekyll,tamouse/jekyll,alfredxing/jekyll,ewinkler/jekyll,SQS2/Test,QuinntyneBrown/jekyll,mixxmac/jekyll,tomasdiez/jekyll,m2candre/jekyll,alex-kovac/jekyll,stomar/jekyll,gencer/jekyll,liukaijv/jekyll,LeuisKen/jekyllcn,tillgrallert/jekyll,saitodisse/jekyll,fulldecent/jekyll,LeuisKen/jekyllcn,thetaxman/jekyll,desidude03/jekyll,tugberkugurlu/jekyll,sanxore/sanxore.github.com,Wirachmat/jekyll,tugberkugurlu/jekyll,isathish/jekyll,wentixiaogege/jekyll,floydpraveen/jekyll,krahman/jekyll,CorainChicago/jekyll,rajrathore/jekyll,fabulousu/jekyll,goragod/jekyll,dangaute/eng,ZDroid/jekyll,darwin/jekyll,AtekiRyu/jekyll,wadaries/jekyll,christophermanning/jekyll,julienbourdeau/jekyll,xiebinhqy/jklly_china,supriyantomaftuh/jekyll,johnnycastilho/jekyll,noikiy/jekyll,penchan1218/jekyllcn,CPVPLachlan/CPVP-Blog,Tiger66639/jekyll,jmepg/jekyll,xiongjungit/jekyll,UniFreak/jekyllcn,mrb/jekyll,mrb/jekyll,schaazzz/jekyll,indraj/jekyll,fulldecent/jekyll,shliujing/jekyll,harrissoerja/jekyll,0x00evil/jekyll,zsyed91/jekyll,gkunwar/gkunwar.github.io,ryanshaw/jekyll,sideci-sample/sideci-sample-jekyll,rebornix/jekyll,dansef/jekyll,Wirachmat/jekyll,0x00evil/jekyll,rlugojr/jekyll,fabulousu/jekyll,jmknoll/jekyll,likong/jekyll,x-way/jekyll,digideskio/jekyll,jekyll/jekyll,jekyll/jekyll,foocoder/jekyll,royalwang/jekyll,eninya/jekyll,doubleday/jekyll,garvitr/jekyll,alfredxing/jekyll,jeffkole/jek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