Added IGUIElement::isMyChild, isPointInside, SEvent.GUIEvent.Element.
Changed setFocus and removeFocus to return bools.
changed quaternion::toAngleAxis to use iszero.
git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@763 dfc29bdd-3216-0410-991c-e03cc46cb475