BUG: core/ufunc: fix assumptions about iterator in execute_fancy_ufunc_loops
BUG: core/ufunc: fix assumptions about iterator in execute_fancy_ufunc_loops

Because the wheremask loop does not write to all elements of the array, it
needs to consider output arrays as READWRITE, in case COPY_IF_OVERLAP makes
temporary copies.

As the iterator may make temporary copies of arrays, make sure to pass those to
__array_prepare__ instead of the originals.

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