Ensure easy rotation of corner-stretched shapes

If corner-stretched shape is pulled to the left, make sure the
rotation step works properly.

src/tuxpaint.c

@@ -2212,6 +2212,8 @@ enum
   SHAPE_TOOL_MODE_DONE
 };
 
+int shape_reverse;
+
 
 int brushflag, xnew, ynew, eraflag, lineflag, magicflag, keybd_flag, keybd_position, keyglobal, initial_y, gen_key_flag,
   ide, activeflag, old_x, old_y;
@@ -5359,6 +5361,8 @@ static void mainloop(void)
 
                           do_shape(shape_start_x, shape_start_y, new_x, new_y, 0, 0);
 
+                          shape_reverse = (new_x < shape_start_x);
+
 
                           /* FIXME: Fix update shape function! */
 
@@ -13256,9 +13260,12 @@ static int shape_rotation(int ctr_x, int ctr_y, int ox, int oy)
 {
   int deg;
 
-
   deg = (atan2(oy - ctr_y, ox - ctr_x) * 180 / M_PI);
 
+  if (shape_reverse && shape_mode == SHAPEMODE_CORNER) {
+    deg = (deg + 180) % 360;
+  }
+
   if (shape_radius < 50)
     deg = ((deg - 15) / 30) * 30;
   else if (shape_radius < 100)