Improve highlighting of commented code

[mookid]

On the following example:

@
-fn func(a,b,c) {
-  x = g(a,b)
-  y = if x {
-          h(b,c)
-      } else {
-          0
-      }
-  return x + y
-}
+// fn func(a,b,c) {
+//   x = g(a,b)
+//   y = if x {
+//           h(b,c)
+//       } else {
+//           0
+//       }
+//   return x + y
+// }

diffr displays the diff like that:

which is correct, but the highlighting of the whitespace-only tokens is distracting.