Adding two new driver types for each platform. Fl_..._System_Drivers exist once per application and provide an interface for to file and filename handling, timers, locking, multithreading, etc. .
The Fl_..._Window_Driver class is instantiated once for every window in the system and corresponds closely to (and actually inherits from) Fl_X. The difference now is, that there is one Fl_X/Fl_Window_Driver base class, and one platform version that derives from it.
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3-porting@11193 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
