Copter: allow arming in GUIDED only from GCS

Also changed mode_allows_arming function to accept arming_from_gcs param
Also remove AUTOTUNE from arming list

ArduCopter/flight_mode.pde

@@ -267,8 +267,10 @@ static bool manual_flight_mode(uint8_t mode) {
     return false;
 }
 
-static bool mode_allows_arming(uint8_t mode) {
-    if (manual_flight_mode(mode) || mode == LOITER || mode == ALT_HOLD || mode == POSHOLD || mode == AUTOTUNE || mode == GUIDED) {
+// mode_allows_arming - returns true if vehicle can be armed in the specified mode
+//  arming_from_gcs should be set to true if the arming request comes from the ground station
+static bool mode_allows_arming(uint8_t mode, bool arming_from_gcs) {
+    if (manual_flight_mode(mode) || mode == LOITER || mode == ALT_HOLD || mode == POSHOLD || (arming_from_gcs && mode == GUIDED)) {
         return true;
     }
     return false;

ArduCopter/motors.pde

@@ -504,10 +504,10 @@ static bool pre_arm_gps_checks(bool display_failure)
 
 // arm_checks - perform final checks before arming
 // always called just before arming.  Return true if ok to arm
-static bool arm_checks(bool display_failure, bool request_from_gcs)
+static bool arm_checks(bool display_failure, bool arming_from_gcs)
 {
     // always check if the current mode allows arming
-    if (!mode_allows_arming(control_mode) || (!request_from_gcs && control_mode == GUIDED)) {
+    if (!mode_allows_arming(control_mode, arming_from_gcs)) {
         if (display_failure) {
             gcs_send_text_P(SEVERITY_HIGH,PSTR("Arm: Mode not armable"));
         }