made using completion respect type constraints and added typer_globals.global_using

git-svn-id: http://haxe.googlecode.com/svn/trunk@6072 f16182fa-f095-11de-8f43-4547254af6c6
delay underlying type vs. from/to check (fixed issue #1446)

git-svn-id: http://haxe.googlecode.com/svn/trunk@6073 f16182fa-f095-11de-8f43-4547254af6c6