r=vidur. 18889. PNG images weren't being registered (x-png that is) for viewing by layout, now they are

layout/build/nsLayoutDLF.cpp

@@ -75,6 +75,7 @@ static char* gImageTypes[] = {
   "image/gif",
   "image/jpeg",
   "image/png",
+  "image/x-png",
   "image/x-art",
   "image/x-jg",
   0