Copter: add dataflash error for GPS glitch

ArduCopter/ArduCopter.pde

@@ -1390,7 +1390,14 @@ static void update_GPS(void)
 
         // run glitch protection and update AP_Notify
         gps_glitch.check_position();
-        AP_Notify::flags.gps_glitching = gps_glitch.glitching();
+        if (AP_Notify::flags.gps_glitching != gps_glitch.glitching()) {
+            if (gps_glitch.glitching()) {
+                Log_Write_Error(ERROR_SUBSYSTEM_GPS, ERROR_CODE_GPS_GLITCH);
+            }else{
+                Log_Write_Error(ERROR_SUBSYSTEM_GPS, ERROR_CODE_ERROR_RESOLVED);
+            }
+            AP_Notify::flags.gps_glitching = gps_glitch.glitching();
+        }
 
         // check if we can initialise home yet
         if (!ap.home_is_set) {

ArduCopter/defines.h

@@ -436,6 +436,7 @@ enum ap_message {
 #define ERROR_SUBSYSTEM_FAILSAFE_GCS        8
 #define ERROR_SUBSYSTEM_FAILSAFE_FENCE      9
 #define ERROR_SUBSYSTEM_FLGHT_MODE          10
+#define ERROR_SUBSYSTEM_GPS                 11
 // general error codes
 #define ERROR_CODE_ERROR_RESOLVED           0
 #define ERROR_CODE_FAILED_TO_INITIALISE     1
@@ -446,6 +447,8 @@ enum ap_message {
 #define ERROR_CODE_FAILSAFE_OCCURRED        1
 // subsystem specific error codes -- compass
 #define ERROR_CODE_COMPASS_FAILED_TO_READ   2
+// subsystem specific error codes -- gps
+#define ERROR_CODE_GPS_GLITCH               2