Fixed bug where Classifier wouldn't detect that the new underline span

it was being asked to highlight was identical to the old.  This caused
it to send out spurious (and fairly constant) layouts.  In addition
to the perf implications, this caused two annoying bugs:

1) You couldn't ctrl-click on an underlined token when there was a marker of
   some sort over the text (breakpoint, highlight-matching-identifier, etc.)
2) If you were trying to activate a smart tag with ctrl+. the smart tag would
   open and then immediately close.

Classifier.cs

@@ -98,6 +98,9 @@ public void SetUnderlineSpan(SnapshotSpan? span)
             if (!oldSpan.HasValue && !_underlineSpan.HasValue)
                 return;
 
+            else if (oldSpan.HasValue && _underlineSpan.HasValue && oldSpan == _underlineSpan)
+                return;
+
             if (!_underlineSpan.HasValue)
             {
                 this.SendEvent(oldSpan.Value);

GoToDefMouseHandler.cs

@@ -287,4 +287,4 @@ bool DispatchGoToDef()
 
         #endregion
     }
-}
+}