added proper cascade for deletes
added proper cascade for deletes

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