Fix for reflecting mysql keys that have USING
Fix for reflecting mysql keys that have USING

davidfraser/sqlalchemy,robin900/sqlalchemy,davidjb/sqlalchemy,bdupharm/sqlalchemy,elelianghh/sqlalchemy,inspirehep/sqlalchemy,EvaSDK/sqlalchemy,elelianghh/sqlalchemy,dstufft/sqlalchemy,brianv0/sqlalchemy,davidfraser/sqlalchemy,itkovian/sqlalchemy,276361270/sqlalchemy,robin900/sqlalchemy,davidjb/sqlalchemy,sandan/sqlalchemy,Akrog/sqlalchemy,j5int/sqlalchemy,inspirehep/sqlalchemy,olemis/sqlalchemy,epa/sqlalchemy,wfxiang08/sqlalchemy,zzzeek/sqlalchemy,brianv0/sqlalchemy,bootandy/sqlalchemy,hsum/sqlalchemy,j5int/sqlalchemy,sandan/sqlalchemy,EvaSDK/sqlalchemy,wfxiang08/sqlalchemy,alex/sqlalchemy,wujuguang/sqlalchemy,halfcrazy/sqlalchemy,itkovian/sqlalchemy,alex/sqlalchemy,hsum/sqlalchemy,epa/sqlalchemy,graingert/sqlalchemy,Cito/sqlalchemy,276361270/sqlalchemy,wujuguang/sqlalchemy,bootandy/sqlalchemy,ThiefMaster/sqlalchemy,graingert/sqlalchemy,pdufour/sqlalchemy,monetate/sqlalchemy,dstufft/sqlalchemy,sqlalchemy/sqlalchemy,monetate/sqlalchemy,halfcrazy/sqlalchemy,Akrog/sqlalchemy,ThiefMaster/sqlalchemy,Cito/sqlalchemy,WinterNis/sqlalchemy,Cito/sqlalchemy,olemis/sqlalchemy,bdupharm/sqlalchemy,WinterNis/sqlalchemy,alex/sqlalchemy,pdufour/sqlalchemy