extensive orb_advert_t fixes

The calls to orb_advertise were being mishandled throughout the code.
There were ::close() calls on memory pointers, there were checks
against < 0 when it is a pointer to a object and values larger than
0x7ffffffff are valid. Some places orb_advert_t variables were
being initialized as 0 other places as -1.

The orb_advert_t type was changed to uintptr_t so the pointer value
would not be wrapped as a negative number. This was causing a failure
on ARM.

Tests for < 0 were changed to == 0 since a null pointer is the valid
representation for error, or uninitialized.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/sensors/sensors.cpp

@@ -517,13 +517,13 @@ Sensors::Sensors() :
 	_manual_control_sub(-1),
 
 	/* publications */
-	_sensor_pub(-1),
-	_manual_control_pub(-1),
-	_actuator_group_3_pub(-1),
-	_rc_pub(-1),
-	_battery_pub(-1),
-	_airspeed_pub(-1),
-	_diff_pres_pub(-1),
+	_sensor_pub(0),
+	_manual_control_pub(0),
+	_actuator_group_3_pub(0),
+	_rc_pub(0),
+	_battery_pub(0),
+	_airspeed_pub(0),
+	_diff_pres_pub(0),
 
 	/* performance counters */
 	_loop_perf(perf_alloc(PC_ELAPSED, "sensor task update")),