added check in SessionTrans.begin() that the underlying unit of work is still the current uow
added check in SessionTrans.begin() that the underlying unit of work is still the current uow

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