added backwards compatability for pandas term parsing so we can work wit...

@quasiben @spearsem 

pandas 0.13 breaks old style pytables query syntax, I ripped out one of their backwards compat functions so we could use it

few changes
- it's an instance method, I made it a non-instance method
- for some reason "{0}".format(x) does not work for numpy datetimes, so I had to call str(x) on it first

The reason this is necessary, is that pandas fixed their backwards compatibility logic with the old query syntax in 0.14, but 0.13 is out and is broken, pydata/pandas#6313