Fixed a bug found by Maxime Muller:

> during event void AdcResource.granted[uint8_t client]()
> If your sref is not REFERENCE_VREFplus_AVss ||
> REFERENCE_VREFplus_VREFnegterm
> then you will never call Refvolt_1/2_5V.start()
> Now while releasing the resource, imho, we should do the same check
> else we end up with a post switchOff() loop
> as call RefVolt_1_5V.stop() will fail.

Fix: changed the "owner" variable to "syncOwner", which is now only modified in sync (task) context and have the async path "parallel" and unaffecting the "syncOwner" variable (hard to explain, have a look at the diff) - there's a test app in tinyos-2.x/apps/tests/msp430/Adc12.