Support non-standard ids for Users.
Support non-standard ids for Users.

Custom user models might have different id field names. Using pk is recommended anyway.
rmgorman/django-guardian,calvinpy/django-guardian,hunter007/django-guardian,calvinpy/django-guardian,EnHatch/django-guardian,brianmay/django-guardian,vitan/django-guardian,rfleschenberg/django-guardian,lukaszb/django-guardian,EnHatch/django-guardian,alexshin/django-guardian,TailorDev/django-guardian,brianmay/django-guardian,hunter007/django-guardian,brianmay/django-guardian,sindrig/django-guardian,infoxchange/django-guardian,vitan/django-guardian,frwickst/django-guardian,lukaszb/django-guardian,infoxchange/django-guardian,giocalitri/django-guardian,infoxchange/django-guardian,patgmiller/django-guardian,rfleschenberg/django-guardian,sindrig/django-guardian,vovanbo/django-guardian,RDXT/django-guardian,onaio/django-guardian,thedrow/django-guardian,EnHatch/django-guardian,lukaszb/django-guardian,giocalitri/django-guardian,hunter007/django-guardian,EnHatch/django-guardian,rmgorman/django-guardian,giocalitri/django-guardian,frwickst/django-guardian,sindrig/django-guardian,alexshin/django-guardian,thedrow/django-guardian,vitan/django-guardian,vovanbo/django-guardian,benkonrath/django-guardian,frwickst/django-guardian,rfleschenberg/django-guardian,calvinpy/django-guardian,benkonrath/django-guardian,TailorDev/django-guardian,TailorDev/django-guardian,alexshin/django-guardian,patgmiller/django-guardian,benkonrath/django-guardian,thedrow/django-guardian,onaio/django-guardian,thedrow/django-guardian,RDXT/django-guardian,onaio/django-guardian,RDXT/django-guardian,vovanbo/django-guardian,vitan/django-guardian,rmgorman/django-guardian,patgmiller/django-guardian