Fix sessionmaker.__repr__
Fix sessionmaker.__repr__

A comma separating 'class_' from the other args. It's still there even when kw is empty, which is syntactically correct.
j5int/sqlalchemy,bdupharm/sqlalchemy,brianv0/sqlalchemy,hsum/sqlalchemy,inspirehep/sqlalchemy,inspirehep/sqlalchemy,276361270/sqlalchemy,halfcrazy/sqlalchemy,monetate/sqlalchemy,dstufft/sqlalchemy,davidjb/sqlalchemy,wfxiang08/sqlalchemy,elelianghh/sqlalchemy,davidfraser/sqlalchemy,bootandy/sqlalchemy,276361270/sqlalchemy,Cito/sqlalchemy,epa/sqlalchemy,Akrog/sqlalchemy,pdufour/sqlalchemy,monetate/sqlalchemy,robin900/sqlalchemy,sqlalchemy/sqlalchemy,ThiefMaster/sqlalchemy,graingert/sqlalchemy,brianv0/sqlalchemy,halfcrazy/sqlalchemy,wujuguang/sqlalchemy,j5int/sqlalchemy,itkovian/sqlalchemy,wujuguang/sqlalchemy,WinterNis/sqlalchemy,davidjb/sqlalchemy,WinterNis/sqlalchemy,davidfraser/sqlalchemy,hsum/sqlalchemy,epa/sqlalchemy,sandan/sqlalchemy,graingert/sqlalchemy,Akrog/sqlalchemy,EvaSDK/sqlalchemy,bdupharm/sqlalchemy,wfxiang08/sqlalchemy,robin900/sqlalchemy,zzzeek/sqlalchemy,pdufour/sqlalchemy,sandan/sqlalchemy,ThiefMaster/sqlalchemy,olemis/sqlalchemy,olemis/sqlalchemy,Cito/sqlalchemy,bootandy/sqlalchemy,Cito/sqlalchemy,elelianghh/sqlalchemy,EvaSDK/sqlalchemy,itkovian/sqlalchemy,dstufft/sqlalchemy