unit description should not be an unrelated unit

[crotwell]

Example from stationxml docs:

http://docs.fdsn.org/projects/stationxml/en/latest/response.html#ysi-44031-thermistor

<Stage number="5">
              <Coefficients name=" DECIMATION">
              <InputUnits>
                 <Name>counts</Name>
                 <Description>Volts</Description>
              </InputUnits>

Checking description is probably too hard in general, which is why I think description should be omitted if the unit is SI. But perhaps checking to see if the Description actually is a unit and that it doesn't match the name would be useful.

Alternatively, a warn if unit has a description and unit Name is in the list of well known units to the validator to discourage using Description when it really doesn't add anything?