Copter: setting ESC param to 2 skips high throttle check

This allows the all-at-once ESC calibration to be performed on a setup
in which the RC input takes some time to come online.

ArduCopter/Parameters.pde

@@ -343,7 +343,7 @@ const AP_Param::Info var_info[] PROGMEM = {
     // @DisplayName: ESC Calibration
     // @Description: Controls whether ArduCopter will enter ESC calibration on the next restart.  Do not adjust this parameter manually.
     // @User: Advanced
-    // @Values: 0:Normal Start-up,1:Start-up in ESC Calibration mode
+    // @Values: 0:Normal Start-up, 1:Start-up in ESC Calibration mode if throttle high, 2:Start-up in ESC Calibration mode regardless of throttle
     GSCALAR(esc_calibrate, "ESC",                   0),
 
     // @Param: TUNE

ArduCopter/radio.pde

@@ -57,7 +57,7 @@ static void init_rc_out()
     g.rc_3.set_range_out(0,1000);
 
     // full throttle means to enter ESC calibration
-    if(g.rc_3.control_in >= (g.throttle_max - 50)) {
+    if(g.rc_3.control_in >= (g.throttle_max - 50) || (g.esc_calibrate == 2)) {
         if(g.esc_calibrate == 0) {
             // we will enter esc_calibrate mode on next reboot
             g.esc_calibrate.set_and_save(1);