changed behaviour of IGUIElement::OnEvent so it doesn't always absorb events, and added getAbsoluteClippingRect.
fixed tooltip text on file open dialog's close button.
added some managed marshalling bugfix things where I missed them earlier.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@751 dfc29bdd-3216-0410-991c-e03cc46cb475