AP_Mission: added truncate() function

Used when loading a mission while flying

Pair-Programmed-With: Randy Mackay <rmackay9@yahoo.com>

libraries/AP_Mission/AP_Mission.cpp

@@ -113,6 +113,15 @@ bool AP_Mission::clear()
     return true;
 }
 
+
+/// trucate - trunacte any mission items beyond index
+void AP_Mission::truncate(uint16_t index)
+{
+    if (_cmd_total > index) {        
+        _cmd_total.set_and_save(index);
+    }
+}
+
 /// update - ensures the command queues are loaded with the next command and calls main programs command_init and command_verify functions to progress the mission
 ///     should be called at 10hz or higher
 void AP_Mission::update()

libraries/AP_Mission/AP_Mission.h

@@ -130,6 +130,9 @@ public:
     ///     returns true if mission was running so it could not be cleared
     bool clear();
 
+    /// truncate - truncate any mission items beyond given index
+    void truncate(uint16_t index);
+
     /// update - ensures the command queues are loaded with the next command and calls main programs command_init and command_verify functions to progress the mission
     ///     should be called at 10hz or higher
     void update();