#13 Need warning for invalid devConfig.xml string entries

[ppanish]

There is currently no verification or warning that the device strings in devConfig.xml are valid entries in the sysFuncDesc_data array. As a result, an incorrectly formatted xml file will be blindly accepted and the device assgned to an inaccessible identifier. Both the owAssignTempSensors() and the owAssignPIODevices() functions should be modified to verify these identifiers.

If possible this should be added as a pure virtual function to owDevice with specific implementations in owTempSensor and owPIODevice classes.