gitk: Provide a 32x32 window icon based on the git logo

This simply expands the 16x16 logo image to 32x32 and provides it as
an alternative icon image.
Signed-off-by: NStephen Boyd <bebarino@gmail.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

gitk

@@ -10902,7 +10902,10 @@ catch {
     gitlogo copy gitlogoplus  -to 11 9
     image delete gitlogoplus
 
-    wm iconphoto . -default gitlogo
+    image create photo gitlogo32    -width 32 -height 32
+    gitlogo32 copy gitlogo -zoom 2 2
+
+    wm iconphoto . -default gitlogo gitlogo32
 }
 # wait for the window to become visible
 tkwait visibility .