* made MonitorWin thread wait until associated WinBorder is hidden
and RootLayer's lock is acquired.
RootLayer.cpp:
* added 2 public methods for calculating visible regions.
ALL:
* all previous 'Invalidate' methods now call RootLayer's ones.
That's it, all region calculations are done in the context of the
high priority thread: WorkingThread.
git-svn-id: file:///srv/svn/repos/haiku/trunk/current@10961 a95241bf-73f2-0310-859d-f6bbb57e9c96