Fixed a PostScript error triggered when calling 
Fl_PostScript_Graphics_Driver::arc(int x, int y, int w, int h, double a1, double a2)
with w == 1 or h == 1, as reported in 
http://www.fltk.org/newsgroups.php?s28125+gfltk.general+v28133


git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@9950 ea41ed52-d2ee-0310-a9c1-e6b18d33e121