Plane: changed TKOFF_THR_DELAY default to 2

this makes it safer for hand launch with pusher props

ArduPlane/Attitude.pde

@@ -475,6 +475,7 @@ static bool auto_takeoff_check(void)
         goto no_launch;
     }
 
+    // we've reached the acceleration threshold, so start the timer
     if (!launchTimerStarted) {
         launchTimerStarted = true;
         last_tkoff_arm_time = now;

ArduPlane/Parameters.pde

@@ -113,7 +113,7 @@ const AP_Param::Info var_info[] PROGMEM = {
     // @Range: 0 15
     // @Increment: 1
     // @User: User
-    GSCALAR(takeoff_throttle_delay,     "TKOFF_THR_DELAY",  0),
+    GSCALAR(takeoff_throttle_delay,     "TKOFF_THR_DELAY",  2),
 
     // @Param: LEVEL_ROLL_LIMIT
     // @DisplayName: Level flight roll limit