ENH: Use subprocess, not execv
ENH: Use subprocess, not execv

This means that the `SHELL` variable does not need to be a full path. execvp
would also have solved this

It also means that this works inside git bash on windows. Previously, it was
confused by windows file paths.

Eric89GXL/numpy,behzadnouri/numpy,rgommers/numpy,jakirkham/numpy,tynn/numpy,mhvk/numpy,bringingheavendown/numpy,WarrenWeckesser/numpy,pbrod/numpy,MSeifert04/numpy,tynn/numpy,MSeifert04/numpy,anntzer/numpy,grlee77/numpy,grlee77/numpy,anntzer/numpy,solarjoe/numpy,Eric89GXL/numpy,simongibbons/numpy,chatcannon/numpy,madphysicist/numpy,simongibbons/numpy,behzadnouri/numpy,endolith/numpy,jakirkham/numpy,shoyer/numpy,Eric89GXL/numpy,MSeifert04/numpy,pdebuyl/numpy,mattip/numpy,jorisvandenbossche/numpy,mhvk/numpy,charris/numpy,numpy/numpy,endolith/numpy,ahaldane/numpy,jorisvandenbossche/numpy,b-carter/numpy,numpy/numpy,jakirkham/numpy,ahaldane/numpy,b-carter/numpy,MSeifert04/numpy,rgommers/numpy,shoyer/numpy,Eric89GXL/numpy,ahaldane/numpy,jorisvandenbossche/numpy,WarrenWeckesser/numpy,pbrod/numpy,chatcannon/numpy,simongibbons/numpy,WarrenWeckesser/numpy,simongibbons/numpy,b-carter/numpy,gfyoung/numpy,gfyoung/numpy,anntzer/numpy,WarrenWeckesser/numpy,pizzathief/numpy,numpy/numpy,seberg/numpy,mattip/numpy,mhvk/numpy,charris/numpy,pbrod/numpy,abalkin/numpy,jorisvandenbossche/numpy,pbrod/numpy,pizzathief/numpy,grlee77/numpy,pizzathief/numpy,rgommers/numpy,solarjoe/numpy,rgommers/numpy,mattip/numpy,pizzathief/numpy,madphysicist/numpy,ahaldane/numpy,charris/numpy,tynn/numpy,MSeifert04/numpy,pdebuyl/numpy,numpy/numpy,jakirkham/numpy,abalkin/numpy,charris/numpy,shoyer/numpy,ahaldane/numpy,seberg/numpy,madphysicist/numpy,gfyoung/numpy,jorisvandenbossche/numpy,solarjoe/numpy,anntzer/numpy,mhvk/numpy,grlee77/numpy,chatcannon/numpy,abalkin/numpy,bringingheavendown/numpy,seberg/numpy,madphysicist/numpy,pizzathief/numpy,WarrenWeckesser/numpy,mhvk/numpy,seberg/numpy,pbrod/numpy,shoyer/numpy,jakirkham/numpy,pdebuyl/numpy,shoyer/numpy,grlee77/numpy,mattip/numpy,madphysicist/numpy,pdebuyl/numpy,simongibbons/numpy,endolith/numpy,behzadnouri/numpy,endolith/numpy,bringingheavendown/numpy