tooltip support for the menu (only the credits dialog has a tooltip as of now)

tooltip support for the menu (only the credits dialog has a tooltip as of now)

To assign a tooltip to a class, add:
	ATTRIB(CLASSNAMEGOESHERE, tooltip, string, "Information about who was involved in making this game.")
to the class declaration

To assign a tooltip to a button or label or other item, add:
	e.tooltip = "Information about who was involved in making this game.";
behind the "e = make......" function call.

git-svn-id: svn://svn.icculus.org/nexuiz/trunk@6816 f962a42d-fe04-0410-a3ab-8c8b0445ebaa