Fix another 2 bugs in CGUITreeView: 
- Irrlicht elements can't just set ID's otherwise user-elements stop working.
  So anyone who had gui-elements not working with ID 0 or 1 - you probably had a guitree somewhere.
  Those ID's were not even used...
- Make the horizontal scrollbar (mostly) work. Selection still messed up, but was that way before and least h-scrolling works now somewhat (did nothing before).
There are more bugs in this gui-element - like that it doesn't draw the last line regularly. 
But I have no more time, nor motiviation for this now (not the first time finding pretty obvious bugs in the treeview. 
I wish that d*mn thing would never had been checked in. Or the original author would at least have tested it or cared about maintaince!).


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4758 dfc29bdd-3216-0410-991c-e03cc46cb475
Focus behavior of IGUIEnvironment now controllable (right-click focus, mouse-over focus). Disabled elements no longer get the focus unless users enforce it.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4759 dfc29bdd-3216-0410-991c-e03cc46cb475
Add header which I forgot in last check-in, sorry!


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4760 dfc29bdd-3216-0410-991c-e03cc46cb475
Add new EFocusFlags.h also to project filess.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4761 dfc29bdd-3216-0410-991c-e03cc46cb475