Fix an architectural issue with the ORB that prevented publication from interrupt context.

ORB topic advertisements are now global handles that can be used in any context.  It is still possible to open a topic node as a publisher, but it's not the default.  As a consequence, the type of the handle returned from orb_advertise has changed; all other API remains the same.

apps/drivers/drv_orb_dev.h

@@ -81,4 +81,7 @@
 /** Set the minimum interval at which the topic can be seen to be updated for this subscription */
 #define ORBIOCSETINTERVAL	_ORBIOC(12)
 
+/** Get the global advertiser handle for the topic */
+#define ORBIOCGADVERTISER	_ORBIOC(13)
+
 #endif /* _DRV_UORB_H */

apps/drivers/hmc5883/hmc5883.cpp

@@ -147,7 +147,7 @@ private:
 	mag_scale		_scale;
 	bool			_collect_phase;
 
-	int			_mag_topic;
+	orb_advert_t		_mag_topic;
 
 	unsigned		_reads;
 	unsigned		_measure_errors;

apps/drivers/mpu6000/mpu6000.cpp

@@ -181,12 +181,12 @@ private:
 	struct accel_report	_accel_report;
 	struct accel_scale	_accel_scale;
 	float			_accel_range_scale;
-	int			_accel_topic;
+	orb_advert_t		_accel_topic;
 
 	struct gyro_report	_gyro_report;
 	struct gyro_scale	_gyro_scale;
 	float			_gyro_range_scale;
-	int			_gyro_topic;
+	orb_advert_t		_gyro_topic;
 
 	unsigned		_reads;
 	perf_counter_t		_sample_perf;

apps/drivers/ms5611/ms5611.cpp

@@ -125,7 +125,7 @@ private:
 	int32_t			_dT;
 	int64_t			_temp64;
 
-	int			_baro_topic;
+	orb_advert_t		_baro_topic;
 
 	unsigned		_reads;
 	unsigned		_measure_errors;