Added a versioning system to the config files

Marlin/Configuration.h

 #ifndef CONFIGURATION_H
 #define CONFIGURATION_H
 
+/**
+ *
+ *  ***********************************
+ *  **  ATTENTION TO ALL DEVELOPERS  **
+ *  ***********************************
+ *
+ * You must increment this version number for every significant change such as,
+ * but not limited to: ADD, DELETE RENAME OR REPURPOSE any directive/option.
+ *
+ * Note: Update also Default_Version.h !
+ */
+#define CONFIGURATION_H_VERSION 1
+
 #include "boards.h"
 #include "macros.h"
 

Marlin/Configuration_adv.h

 #ifndef CONFIGURATION_ADV_H
 #define CONFIGURATION_ADV_H
 
+/**
+ *
+ *  ***********************************
+ *  **  ATTENTION TO ALL DEVELOPERS  **
+ *  ***********************************
+ *
+ * You must increment this version number for every significant change such as,
+ * but not limited to: ADD, DELETE RENAME OR REPURPOSE any directive/option.
+ *
+ * Note: Update also Default_Version.h !
+ */
+#define CONFIGURATION_ADV_H_VERSION 1
+
 #include "Conditionals.h"
 
 // @section temperature

Marlin/SanityCheck.h

 #endif
 
 /**
+ * We try our best to include sanity checks for all the changes configuration
+ * directives because people have a tendency to use outdated config files with
+ * the bleding edge source code, but sometimes this is not enough. This check
+ * will force a minimum config file revision, otherwise Marlin will not build.
+ */
+#if ! defined(CONFIGURATION_H_VERSION) || CONFIGURATION_H_VERSION < REQUIRED_CONFIGURATION_H_VERSION
+  #error You are using an old Configuration.h file, updated it before building Marlin.
+#endif
+
+#if ! defined(CONFIGURATION_ADV_H_VERSION) || CONFIGURATION_ADV_H_VERSION < REQUIRED_CONFIGURATION_ADV_H_VERSION
+  #error You are using an old Configuration_adv.h file, updated it before building Marlin.
+#endif
+
+/**
  * Marlin release, version and default string
  */
 #ifndef SHORT_BUILD_VERSION

Marlin/Version.h

 #define STRING_DISTRIBUTION_DATE "2016-04-27 12:00"
 
 /**
+ * Required minimum Configuration.h and Configuration_adv.h file versions.
+ *
+ * You must increment this version number for every significant change such as,
+ * but not limited to: ADD, DELETE RENAME OR REPURPOSE any directive/option on
+ * the configuration files.
+ */
+#define REQUIRED_CONFIGURATION_H_VERSION 1
+#define REQUIRED_CONFIGURATION_ADV_H_VERSION 1
+
+/**
  * @todo: Missing documentation block
  */
 #define PROTOCOL_VERSION "1.0"