do not allow transitive unification of abstracts that have implementations (fixed issue #1406)

git-svn-id: http://haxe.googlecode.com/svn/trunk@5917 f16182fa-f095-11de-8f43-4547254af6c6
changed haxe.EnumFlags to abstract and added specification

git-svn-id: http://haxe.googlecode.com/svn/trunk@5918 f16182fa-f095-11de-8f43-4547254af6c6
I've just noticed that I never committed this

git-svn-id: http://haxe.googlecode.com/svn/trunk@5919 f16182fa-f095-11de-8f43-4547254af6c6