1999 Data Fetch Results in Incorrect Units

The recent inclusion of 1999 data into the archive seems to be associated with incorrect/inconsistent units.  Example:

In [316]: x = fetch.Msid('PM1THV1T','1999:200', stat='5min')
In [317]: x.plot()
In [318]: x = fetch.Msid('PM1THV1T','2000:001', stat='5min')
In [319]: x.plot('r')

Yields the following plot:
![scrap](https://cloud.githubusercontent.com/assets/1004631/3107085/d3b63700-e681-11e3-92c7-6377c2cb2178.png)

I believe the 1999+ data is in Kelvin whereas the 2000+ data is in Fahrenheit.  However, an examination of "x.unit" for both yields "DEGF".

@matthewdahmer