New admin command to check Pyro etc. is installed.

Some users have a lot of trouble figuring out if they've installed everything properly. 

```
% cylc admin check-software
Checking for Python >= 2.5 ... found 2.6.8 ... ok
Checking for non-Python packages:
 + Graphviz ... ok
 + sqlite ... ok
Checking for Python packages:
 + Pyro-3 ... ok
 + Jinja2 ... ok
 + pygraphviz ... ok
 + pygtk ... ok
```