Fixed bug with tab controls not absorbing a mouse-down but expecting to have the focus in a mouse-up,  reported by christianclavet.
Windows are now brought to the front when any of their children are focused.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@1212 dfc29bdd-3216-0410-991c-e03cc46cb475