check if the user model is already registered
check if the user model is already registered

Fix usage of overwriting the UserProfileAdmin because it will be under mezzanine.accounts in INSTALLED_APPS.
webounty/mezzanine,Skytorn86/mezzanine,viaregio/mezzanine,dekomote/mezzanine-modeltranslation-backport,joshcartme/mezzanine,frankchin/mezzanine,AlexHill/mezzanine,eino-makitalo/mezzanine,vladir/mezzanine,stephenmcd/mezzanine,industrydive/mezzanine,wyzex/mezzanine,douglaskastle/mezzanine,geodesign/mezzanine,adrian-the-git/mezzanine,Kniyl/mezzanine,christianwgd/mezzanine,spookylukey/mezzanine,emile2016/mezzanine,frankier/mezzanine,dovydas/mezzanine,Skytorn86/mezzanine,adrian-the-git/mezzanine,Cajoline/mezzanine,vladir/mezzanine,agepoly/mezzanine,fusionbox/mezzanine,geodesign/mezzanine,sjdines/mezzanine,wbtuomela/mezzanine,eino-makitalo/mezzanine,webounty/mezzanine,SoLoHiC/mezzanine,batpad/mezzanine,agepoly/mezzanine,ryneeverett/mezzanine,ryneeverett/mezzanine,frankier/mezzanine,SoLoHiC/mezzanine,douglaskastle/mezzanine,ZeroXn/mezzanine,saintbird/mezzanine,christianwgd/mezzanine,dsanders11/mezzanine,dustinrb/mezzanine,nikolas/mezzanine,theclanks/mezzanine,Kniyl/mezzanine,wbtuomela/mezzanine,biomassives/mezzanine,sjuxax/mezzanine,cccs-web/mezzanine,stephenmcd/mezzanine,readevalprint/mezzanine,damnfine/mezzanine,Cajoline/mezzanine,Cajoline/mezzanine,vladir/mezzanine,adrian-the-git/mezzanine,mush42/mezzanine,industrydive/mezzanine,christianwgd/mezzanine,dustinrb/mezzanine,wbtuomela/mezzanine,biomassives/mezzanine,molokov/mezzanine,jerivas/mezzanine,gradel/mezzanine,fusionbox/mezzanine,mush42/mezzanine,damnfine/mezzanine,dovydas/mezzanine,frankchin/mezzanine,PegasusWang/mezzanine,batpad/mezzanine,dekomote/mezzanine-modeltranslation-backport,molokov/mezzanine,dsanders11/mezzanine,wyzex/mezzanine,promil23/mezzanine,Cicero-Zhao/mezzanine,jerivas/mezzanine,sjuxax/mezzanine,saintbird/mezzanine,dustinrb/mezzanine,PegasusWang/mezzanine,sjdines/mezzanine,viaregio/mezzanine,nikolas/mezzanine,AlexHill/mezzanine,readevalprint/mezzanine,joshcartme/mezzanine,eino-makitalo/mezzanine,frankier/mezzanine,jjz/mezzanine,dsanders11/mezzanine,Cicero-Zhao/mezzanine,sjdines/mezzanine,tuxinhang1989/mezzanine,stephenmcd/mezzanine,sjuxax/mezzanine,ZeroXn/mezzanine,tuxinhang1989/mezzanine,mush42/mezzanine,gradel/mezzanine,Skytorn86/mezzanine,geodesign/mezzanine,dovydas/mezzanine,emile2016/mezzanine,jerivas/mezzanine,PegasusWang/mezzanine,spookylukey/mezzanine,dekomote/mezzanine-modeltranslation-backport,tuxinhang1989/mezzanine,jjz/mezzanine,saintbird/mezzanine,biomassives/mezzanine,nikolas/mezzanine,promil23/mezzanine,gradel/mezzanine,industrydive/mezzanine,SoLoHiC/mezzanine,emile2016/mezzanine,Kniyl/mezzanine,agepoly/mezzanine,molokov/mezzanine,wyzex/mezzanine,webounty/mezzanine,douglaskastle/mezzanine,damnfine/mezzanine,readevalprint/mezzanine,theclanks/mezzanine,theclanks/mezzanine,ZeroXn/mezzanine,cccs-web/mezzanine,viaregio/mezzanine,ryneeverett/mezzanine,frankchin/mezzanine,promil23/mezzanine,spookylukey/mezzanine,joshcartme/mezzanine,jjz/mezzanine