[AstroPy] Dropping support for Numpy 1.4 in astropy

[Tom Aldcroft]

The Astropy project (http://astropy.org) is considering dropping
support for Numpy 1.4 in the next (0.3) release.  Drivers include:

- Masked arrays in 1.4 have a number of issues so that the astropy
Table class does not support missing values in numpy 1.4.
- Travis-CI cannot build numpy 1.4, so testing this configuration is
more difficult.
- Numpy 1.4 doesn't build easily on new platforms like Fedora 18.
- Numpy 1.7 (and soon 1.7.1) is out, so supporting the most recent 3
releases seems sufficient.

If anyone has any objections please raise them now.

Cheers,
Tom A