BUG: more on inplace reductions, fixes #615
BUG: more on inplace reductions, fixes #615

This is a follow up to #7407 and #7466. It fixes an error in the
comments (0 is the output and 1 is the input), moves them around so
they apply to both branches of the if/else, and changes memcpy to
memmove, since the memory segments can be overlapping, as pointed
out by Valgrind in a really old issue.

bertrand-l/numpy,WarrenWeckesser/numpy,tynn/numpy,madphysicist/numpy,pizzathief/numpy,charris/numpy,jakirkham/numpy,tynn/numpy,SiccarPoint/numpy,AustereCuriosity/numpy,shoyer/numpy,mhvk/numpy,pdebuyl/numpy,abalkin/numpy,Eric89GXL/numpy,b-carter/numpy,MSeifert04/numpy,jorisvandenbossche/numpy,madphysicist/numpy,gmcastil/numpy,jakirkham/numpy,mattip/numpy,pbrod/numpy,ahaldane/numpy,pizzathief/numpy,joferkington/numpy,SiccarPoint/numpy,pizzathief/numpy,argriffing/numpy,stuarteberg/numpy,ahaldane/numpy,numpy/numpy,argriffing/numpy,utke1/numpy,tacaswell/numpy,shoyer/numpy,grlee77/numpy,ddasilva/numpy,ddasilva/numpy,bertrand-l/numpy,pdebuyl/numpy,dwillmer/numpy,chatcannon/numpy,jorisvandenbossche/numpy,Eric89GXL/numpy,joferkington/numpy,anntzer/numpy,jakirkham/numpy,b-carter/numpy,skwbc/numpy,abalkin/numpy,jorisvandenbossche/numpy,ssanderson/numpy,utke1/numpy,mattip/numpy,SiccarPoint/numpy,bringingheavendown/numpy,skwbc/numpy,anntzer/numpy,dwillmer/numpy,Eric89GXL/numpy,ContinuumIO/numpy,grlee77/numpy,gfyoung/numpy,rgommers/numpy,seberg/numpy,dwillmer/numpy,mhvk/numpy,seberg/numpy,stuarteberg/numpy,grlee77/numpy,mhvk/numpy,MSeifert04/numpy,WarrenWeckesser/numpy,bringingheavendown/numpy,MSeifert04/numpy,shoyer/numpy,gfyoung/numpy,madphysicist/numpy,WarrenWeckesser/numpy,simongibbons/numpy,numpy/numpy,drasmuss/numpy,solarjoe/numpy,mattip/numpy,seberg/numpy,ContinuumIO/numpy,pdebuyl/numpy,charris/numpy,endolith/numpy,WarrenWeckesser/numpy,jakirkham/numpy,pbrod/numpy,grlee77/numpy,ssanderson/numpy,tacaswell/numpy,grlee77/numpy,b-carter/numpy,solarjoe/numpy,joferkington/numpy,behzadnouri/numpy,dwillmer/numpy,gmcastil/numpy,simongibbons/numpy,numpy/numpy,pdebuyl/numpy,shoyer/numpy,WarrenWeckesser/numpy,stuarteberg/numpy,madphysicist/numpy,ContinuumIO/numpy,rgommers/numpy,anntzer/numpy,jakirkham/numpy,ahaldane/numpy,pbrod/numpy,madphysicist/numpy,solarjoe/numpy,gfyoung/numpy,ddasilva/numpy,charris/numpy,pizzathief/numpy,pbrod/numpy,mattip/numpy,bertrand-l/numpy,gmcastil/numpy,rgommers/numpy,seberg/numpy,maniteja123/numpy,MSeifert04/numpy,tacaswell/numpy,jorisvandenbossche/numpy,drasmuss/numpy,anntzer/numpy,pizzathief/numpy,jorisvandenbossche/numpy,tynn/numpy,kiwifb/numpy,rgommers/numpy,simongibbons/numpy,joferkington/numpy,maniteja123/numpy,simongibbons/numpy,simongibbons/numpy,behzadnouri/numpy,abalkin/numpy,drasmuss/numpy,chatcannon/numpy,AustereCuriosity/numpy,ahaldane/numpy,MSeifert04/numpy,njase/numpy,skwbc/numpy,chatcannon/numpy,kiwifb/numpy,utke1/numpy,numpy/numpy,mhvk/numpy,kiwifb/numpy,ahaldane/numpy,maniteja123/numpy,ssanderson/numpy,mhvk/numpy,behzadnouri/numpy,njase/numpy,endolith/numpy,charris/numpy,AustereCuriosity/numpy,endolith/numpy,njase/numpy,endolith/numpy,bringingheavendown/numpy,shoyer/numpy,stuarteberg/numpy,argriffing/numpy,pbrod/numpy,SiccarPoint/numpy,Eric89GXL/numpy