unification fixes related to GADT

git-svn-id: http://haxe.googlecode.com/svn/trunk@6151 f16182fa-f095-11de-8f43-4547254af6c6
minor

git-svn-id: http://haxe.googlecode.com/svn/trunk@6152 f16182fa-f095-11de-8f43-4547254af6c6