Fix tooltip position

$ diff -u src/macfns.c~ src/macfns.c
--- src/macfns.c~	2012-03-22 12:37:16.000000000 +0200
+++ src/macfns.c	2012-03-22 12:36:15.000000000 +0200
@@ -3509,8 +3509,6 @@
 
   if (INTEGERP (top))
     *root_y = XINT (top);
-  else if (*root_y + XINT (dy) <= 0)
-    *root_y = 0; /* Can happen for negative dy */
   else if (*root_y + XINT (dy) + height
 	   <= x_display_pixel_height (FRAME_MAC_DISPLAY_INFO (f)))
     /* It fits below the pointer */
@@ -3524,8 +3522,6 @@
 
   if (INTEGERP (left))
     *root_x = XINT (left);
-  else if (*root_x + XINT (dx) <= 0)
-    *root_x = 0; /* Can happen for negative dx */
   else if (*root_x + XINT (dx) + width
 	   <= x_display_pixel_width (FRAME_MAC_DISPLAY_INFO (f)))
     /* It fits to the right of the pointer.  */

--------------------------------------------------------------------------------
It happens when second monitor attached on top or left.

+---------------------++----------------+
|		      ||----------------|
|		      ||     main       |
|       second        ||                |
|		      |+----------------+
|		      |
+---------------------+

or

+---------------------+
|		      |
|		      |
|	second        |
|		      |
|      	       	      |
+---------------------+
+----------------+
|----------------|
|      main      |
|                |
+----------------+



Cheers,
Pavlo Martynenko
pavelmart@gmail.com