Add more useful information to testing header

All of these are things that have stumbled us up before, so it's helpful to know about.

```
Platform: Linux-3.8.11-200.fc18.x86_64-x86_64-with-fedora-18-Spherical_Cow

Executable: /home/mdboom/python/bin/python

Full Python Version: 
2.7.3 (default, Aug  9 2012, 17:23:57) 
[GCC 4.7.1 20120720 (Red Hat 4.7.1-5)]

encodings: sys: ascii, locale: ISO-8859-1, filesystem: ISO-8859-1, unicode bits: 20
byteorder: little
float info: dig: 15, mant_dig: 15

Numpy: 1.7.1
Scipy: not available
Matplotlib: 1.2.1
h5py: not available
```