Minor patches to pins files

Marlin/pins_GEN6.h

@@ -51,10 +51,8 @@
  *
  */
 
-#ifndef __AVR_ATmega644P__
+#if !defined(__AVR_ATmega644P__) && !defined(__AVR_ATmega1284P__)
-  #ifndef __AVR_ATmega1284P__
+  #error "Oops!  Make sure you have 'Sanguino' selected from the 'Tools -> Boards' menu."
-    #error "Oops!  Make sure you have 'Sanguino' selected from the 'Tools -> Boards' menu."
-  #endif
 #endif
 
 #ifndef BOARD_NAME

Marlin/pins_GT2560_REV_A_PLUS.h

@@ -26,6 +26,7 @@
 
 #include "pins_GT2560_REV_A.h"
 
+#undef BOARD_NAME
 #define BOARD_NAME  "GT2560 Rev.A+"
 
 #define SERVO0_PIN  11