fixing dcone's checkin

in a enum, certain compilers don't like when the
last item has a ',' so I removed it

Fixing messina's tbox bustage

gfx/public/nsIRenderingContext.h

@@ -73,7 +73,7 @@ typedef enum
 typedef enum
 {
   nsPenMode_kNone   = 0,
-  nsPenMode_kInvert = 1,
+  nsPenMode_kInvert = 1
 } nsPenMode;