Increase range of ComparingUpdateTracker statistics

32 bits are not enough to keep track of all the pixels that might
flow through the system. Expand things to 64 bits, which should cover
all reasonable uses.

common/rfb/ComparingUpdateTracker.h

@@ -50,7 +50,7 @@ namespace rfb {
     bool firstCompare;
     bool enabled;
 
-    rdr::U32 totalPixels, missedPixels;
+    unsigned long long totalPixels, missedPixels;
   };
 
 }