Mac only: centered down arrow for mac.

This helps user's clicking accuracy;
clicks on lower part of the down arrow's geoemtry was being missed.



git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@9554 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

src/Fl_Tree_Prefs.cxx

@@ -72,14 +72,14 @@ static const char *L_close_xpm[] = {
   "...........",
   "...........",
   "...........",
-  "...........",
-  "...........",
   "@@@@@@@@@@@",
   ".@@@@@@@@@.",
   "..@@@@@@@..",
   "...@@@@@...",
   "....@@@....",
-  ".....@....."
+  ".....@.....",
+  "...........",
+  "..........."
 #else /* __APPLE__ */
   "11 11 3 1",
   ".	c #fefefe",