Added SensorManager.getMinDelay()

Exposed the new "min delay" sensor property through native and
java sensor apis. This allows the caller to know what is the
maximum rate at which a sensor can return events, or, if a sensor
works in "update" mode (events returned only when the value changes).

Also augmented SensorManager.regusterSensorEvent() so that it can
accept a value in microsecond in addition to the 4 constants already
defined.

Change-Id: If425e9979892666df8c989d7de3c362230fa19e0
diff --git a/include/gui/SensorEventQueue.h b/include/gui/SensorEventQueue.h
index ad36dac..6581ae3 100644
--- a/include/gui/SensorEventQueue.h
+++ b/include/gui/SensorEventQueue.h
@@ -65,7 +65,7 @@
     status_t setEventRate(Sensor const* sensor, nsecs_t ns) const;
 
     // these are here only to support SensorManager.java
-    status_t enableSensor(int32_t handle, int32_t ms) const;
+    status_t enableSensor(int32_t handle, int32_t us) const;
     status_t disableSensor(int32_t handle) const;
 
 private: