solved some compiler warnings that are now visible in arduino 1.0.

Found a couple of unused variables, that I commented.
Tried to solve the program memory warning message, and failed.

Marlin/MarlinSerial.cpp

@@ -20,6 +20,7 @@
   Modified 28 September 2010 by Mark Sproul
 */
 
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>