Remove 2.0 FL_API defines from threads.h, since that header is not part
of the library.
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.1@1848 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Add threading demo from 2.0, with minor improvements to make the
prime number generation faster/more realistic.
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.1@1823 ea41ed52-d2ee-0310-a9c1-e6b18d33e121