Don't use GCC c++ or g++ compiler to build programs, use gcc instead.

Some more anti-warning stuff...

Added --disable-gl option to disable OpenGL support + check.

Added code to stop the configuration if X11 could not be found.


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.0@1441 ea41ed52-d2ee-0310-a9c1-e6b18d33e121