Fixed RAMPS 1.2 support (Found and fixed by rrhb)

Marlin/Marlin.pde

 
 void loop()
 {
-  if(buflen<3)
+  if(buflen < (BUFSIZE-1))
     get_command();
   #ifdef SDSUPPORT
   card.checkautostart(false);

Marlin/pins.h

 // #define RAMPS_V_1_3
 // #define RAMPS_V_1_0
 
-#ifdef MOTHERBOARD == 33 || MOTHERBOARD == 34
+#if MOTHERBOARD == 33 || MOTHERBOARD == 34
 
 #define X_STEP_PIN         54
 #define X_DIR_PIN          55
 #define PS_ON_PIN          -1
 #define KILL_PIN           -1
 
-
-
 #ifdef RAMPS_V_1_0 // RAMPS_V_1_0
   #define HEATER_0_PIN     12    // RAMPS 1.0
   #define HEATER_BED_PIN   -1    // RAMPS 1.0