APM: fixed mission reset by setting waypoint to zero

this does a full mission reset (equivalent to rebooting)

ArduPlane/commands.pde

@@ -9,6 +9,7 @@ static void init_commands()
     nav_command_ID  = NO_COMMAND;
     non_nav_command_ID      = NO_COMMAND;
     next_nav_command.id     = CMD_BLANK;
+    nav_command_index = 0;
 }
 
 static void update_auto()

ArduPlane/commands_process.pde

@@ -4,7 +4,15 @@
 //----------------------------------------
 void change_command(uint8_t cmd_index)
 {
-    struct Location temp = get_cmd_with_index(cmd_index);
+    struct Location temp;
+
+    if (cmd_index == 0) {
+        init_commands();
+        gcs_send_text_fmt(PSTR("Received Request - reset mission"));
+        return;
+    }
+
+    temp = get_cmd_with_index(cmd_index);
 
     if (temp.id > MAV_CMD_NAV_LAST ) {
         gcs_send_text_P(SEVERITY_LOW,PSTR("Bad Request - cannot change to non-Nav cmd"));

ArduPlane/control_modes.pde

@@ -39,7 +39,7 @@ static void read_control_switch()
         APM_RC.InputCh(g.reset_mission_chan-1) > RESET_SWITCH_CHAN_PWM) {
         // reset to first waypoint in mission
         prev_WP = current_loc;
-        change_command(1);
+        change_command(0);
     }
 
     switch_debouncer = false;