Monkeypatch to allow compatibility with astropy < 0.3.dev4957

PR #1006 in astropy converted `Angle.degrees` -> `Angle.degree` and related plural units.  This PR is intended to monkeypatch astropy units for versions earlier that 0.3.dev4957 so that astroquery can be used with them.  

Presently, it doesn't work - I don't understand the units magic well enough to know what needs monkeypatching.