AP_IMU: added new_data_available() interface

libraries/AP_IMU/AP_IMU_INS.cpp

@@ -235,3 +235,7 @@ AP_IMU_INS::update(void)
 	// always updated
 	return true;
 }
+
+bool AP_IMU_INS::new_data_available(void) {
+    return _ins->new_data_available();
+}

libraries/AP_IMU/AP_IMU_INS.h

@@ -51,6 +51,7 @@ public:
 	virtual void		init_gyro(void (*delay_cb)(unsigned long t) = delay,
                                   void (*flash_leds_cb)(bool on) = NULL);
 	virtual bool		update(void);
+	virtual bool		new_data_available(void);
 
 	// for jason
 	virtual float		gx()				{ return _sensor_cal[0]; }

libraries/AP_IMU/AP_IMU_Shim.h

@@ -37,6 +37,8 @@ public:
 	}
 	//@}
 
+	virtual bool new_data_available(void) { return true; }
+	
 	float		gx()				{ return 0; }
 	float		gy()				{ return 0; }
 	float		gz()				{ return 0; }

libraries/AP_IMU/IMU.cpp

@@ -30,6 +30,7 @@ void IMU::init_gyro(void (*delay_cb)(unsigned long t), void (*flash_leds_cb)(boo
 { }
 
 bool IMU::update(void) { return false; }
+bool IMU::new_data_available(void) { return true; }
 
 float	IMU::gx(void) { return 0.0; }
 float	IMU::gy(void) { return 0.0; }

libraries/AP_IMU/IMU.h

@@ -62,6 +62,9 @@ public:
 	///
 	virtual bool	update(void);
 
+	// true if new data is available from the sensors
+	virtual bool new_data_available(void);
+
 	/// Fetch the current gyro values
 	///
 	/// @returns	vector of rotational rates in radians/sec