improved Date/DateTools specification

git-svn-id: http://haxe.googlecode.com/svn/trunk@6145 f16182fa-f095-11de-8f43-4547254af6c6
use global using only on fully known types

git-svn-id: http://haxe.googlecode.com/svn/trunk@6146 f16182fa-f095-11de-8f43-4547254af6c6