[Dce] make sure we are checking the class that actually has the field

git-svn-id: http://haxe.googlecode.com/svn/trunk@5824 f16182fa-f095-11de-8f43-4547254af6c6
[Dce] keep unknown fields too

git-svn-id: http://haxe.googlecode.com/svn/trunk@5825 f16182fa-f095-11de-8f43-4547254af6c6