AP_BattMonitor: added set_monitoring() API

needed for test sketch

libraries/AP_BattMonitor/AP_BattMonitor.h

@@ -83,6 +83,9 @@ public:
     /// monitoring - returns whether we are monitoring voltage only or voltage and current
     int8_t monitoring() const { return _monitoring; }
 
+    /// monitoring - returns whether we are monitoring voltage only or voltage and current
+    void set_monitoring(uint8_t mon) { _monitoring.set(mon); }
+
     /// Battery voltage.  Initialized to 99 to prevent low voltage events at startup
     float voltage() const { return _voltage; }
 

libraries/AP_BattMonitor/examples/AP_BattMonitor_test/AP_BattMonitor_test.pde

@@ -25,6 +25,7 @@ void setup() {
 
     // initialise the battery monitor
     battery_mon.init();
+    battery_mon.set_monitoring(AP_BATT_MONITOR_VOLTAGE_AND_CURRENT);
 
     hal.scheduler->delay(1000);
     timer = hal.scheduler->millis();