Copter: initialise roll, pitch, yaw modes to stabilize

This fixes a bug in which the stabilize throttle controller would be
non-tilt compensated until the user switched to another flight mode and
back again

ArduCopter/ArduCopter.pde

@@ -656,11 +656,11 @@ static int32_t baro_alt;
 // Each Flight mode is a unique combination of these modes
 //
 // The current desired control scheme for Yaw
-static uint8_t yaw_mode;
+static uint8_t yaw_mode = STABILIZE_YAW;
 // The current desired control scheme for roll and pitch / navigation
-static uint8_t roll_pitch_mode;
+static uint8_t roll_pitch_mode = STABILIZE_RP;
 // The current desired control scheme for altitude hold
-static uint8_t throttle_mode;
+static uint8_t throttle_mode = STABILIZE_THR;
 
 
 ////////////////////////////////////////////////////////////////////////////////

ArduCopter/config.h

@@ -532,6 +532,12 @@
 // Flight mode roll, pitch, yaw, throttle and navigation definitions
 
 // Stabilize Mode
+#ifndef STABILIZE_YAW
+ # define STABILIZE_YAW           	YAW_HOLD
+#endif
+#ifndef STABILIZE_RP
+ # define STABILIZE_RP           	ROLL_PITCH_STABLE
+#endif
 #ifndef STABILIZE_THR
  # define STABILIZE_THR           	THROTTLE_MANUAL_TILT_COMPENSATED
 #endif

ArduCopter/system.pde

@@ -352,8 +352,8 @@ static bool set_mode(uint8_t mode)
 
         case STABILIZE:
             success = true;
-            set_yaw_mode(YAW_HOLD);
-            set_roll_pitch_mode(ROLL_PITCH_STABLE);
+            set_yaw_mode(STABILIZE_YAW);
+            set_roll_pitch_mode(STABILIZE_RP);
             set_throttle_mode(STABILIZE_THR);
             set_nav_mode(NAV_NONE);
             break;