added method to nsIView to get nearest scroll offset.
killed AdjustChildWidgets in nsIView.
lots of painting fixes.
added support for scrolling subviews.
added beginning of back-to-front compositing pass.
views, views with widgets and views with specific clips will now have their
outlines rendered in different colors. to turn this off see the top of nsView.cpp.
git-svn-id: svn://10.0.0.236/trunk@3893 18797224-902f-48f8-a5cc-f745e15eee43