Check registered prims first

git-svn-id: http://hxcpp.googlecode.com/svn/trunk@666 d391954c-4287-11de-baa7-5503b21fc9cb
allow undefined for dll_import

git-svn-id: http://hxcpp.googlecode.com/svn/trunk@667 d391954c-4287-11de-baa7-5503b21fc9cb