check abstract casts when typing if (fixed issue #1845)

git-svn-id: http://haxe.googlecode.com/svn/trunk@6681 f16182fa-f095-11de-8f43-4547254af6c6
error if an @:extern inline constructor cannot be inlined

git-svn-id: http://haxe.googlecode.com/svn/trunk@6682 f16182fa-f095-11de-8f43-4547254af6c6