Mac OS: drawing to windows at each FLTK event loop is now done as normally with Cocoa, that is,
by the [NSView drawRect:] implementation. The system therefore has prepared before the 
adequate graphics context for the window.
This introduces a limitation: it's not possible to call Fl::wait(), Fl::check()
nor Fl::ready() while in the draw() function of a widget. Use an idle callback instead.

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10119 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Added docs to Fl_Tabs as per STR#1174, and some doc improvements.



git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10120 ea41ed52-d2ee-0310-a9c1-e6b18d33e121