Fix forward dataflow unification algorithm to avoid creating extra variables when old ones can be reused.  This solves the infinite loop problem previously encountered
Fix forward dataflow unification algorithm to avoid creating extra variables when old ones can be reused.  This solves the infinite loop problem previously encountered

git-svn-id: 47705994653588c662f4ea400dfe88107361c0e2@8723 dc4e9af1-7f46-4ead-bba6-71afc04862de

swift-lang/swift-t,swift-lang/swift-t,JohnPJenkins/swift-t,blue42u/swift-t,basheersubei/swift-t,swift-lang/swift-t,swift-lang/swift-t,JohnPJenkins/swift-t,swift-lang/swift-t,blue42u/swift-t,JohnPJenkins/swift-t,swift-lang/swift-t,basheersubei/swift-t,blue42u/swift-t,basheersubei/swift-t,basheersubei/swift-t,JohnPJenkins/swift-t,blue42u/swift-t,blue42u/swift-t,JohnPJenkins/swift-t,basheersubei/swift-t,basheersubei/swift-t,basheersubei/swift-t,blue42u/swift-t,JohnPJenkins/swift-t,blue42u/swift-t,JohnPJenkins/swift-t,swift-lang/swift-t