removed nonsensical null-handling (fixed issue #1785)

git-svn-id: http://haxe.googlecode.com/svn/trunk@6593 f16182fa-f095-11de-8f43-4547254af6c6
added unit test for optional enum constructor argument

git-svn-id: http://haxe.googlecode.com/svn/trunk@6594 f16182fa-f095-11de-8f43-4547254af6c6