Declare Python 3.3 support

Python 3.2 won't work as it doesn't support unicode literals.

I'm not sure I need those, actually.  In the bad old PyGTK days when
I didn't understand Unicode as much as I understand it now, all the
strings in memory were UTF-8 encoded, and

  '%-70s %s' % (title, duration)

would align the durations incorrectly in the presence of multibyte
characters.

The fix I applied back then (commit 599da6f7024df777d12e) changed those
to

  u'%-70s %s' % (title, duration)

which, as I now understand, caused the title to be converted from UTF-8
str into unicode (without triggering UnicodeDecodeErrors due to PyGTK's
"helpful" implicit sys.setglobalencoding('UTF-8')).

Nowadays all the strings in memory are already unicode, so we shouldn't
need unicode literals.

Except where we're currently using '{0}'.format(some_unicode), since
that's a latent crash waiting to happen.  Hm.
Explicitly use /usr/bin/python for the wrapper script

Reason: you cannot pip install pygobject into a virtualenv, so you must
use the system Python.

And, hey, with the new Python 3 compat code this should work even for
Arch users.