Fl_Rect.H is no longer included by Fl_Group.H to avoid unnecessary
dependencies on Fl_Rect.H. Currently it is only needed to access the
array returned by the protected method bounds().
Also clarified documentation.
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12827 ea41ed52-d2ee-0310-a9c1-e6b18d33e121