Added code to clear the current font cache when the font face is changed. Now for OS X and X11 as well.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.1@5421 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

src/fl_font_mac.cxx

@@ -264,6 +264,11 @@ int fl_font_ = 0;
 int fl_size_ = 0;
 
 void fl_font(int fnum, int size) {
+  if (fnum==-1) {
+    fl_font_ = 0; 
+    fl_size_ = 0;
+    return;
+  }
   fl_font_ = fnum;
   fl_size_ = size;
   fl_font(find(fnum, size));

src/fl_font_x.cxx

@@ -200,6 +200,10 @@ void *fl_xftfont = 0;
 static GC font_gc;
 
 void fl_font(int fnum, int size) {
+  if (fnum==-1) {
+    fl_font_ = 0; fl_size_ = 0;
+    return;
+  }
   if (fnum == fl_font_ && size == fl_size_) return;
   fl_font_ = fnum; fl_size_ = size;
   Fl_FontSize* f = find(fnum, size);