A few notes:

* I went ahead and removed theano/misc/hg_version_hook.sh. It
  is not functional now, so I inferred that no one cares about
  it (file a new issue if I'm wrong!). It'll be in the history,
  should we ever want to write a git hook replacement for it.
* I made some minor whitespace fixes, including collapsing the
  unnecessary double-depth try/finally.
* I think that the _minimal_ext_cmd isn't needed, but I left it in.
* Why not do direct substitution into full_version, instead of
  writing code to do Python substitution again? Left it as is for
  now, in case there's a good reason...