Encourage a run of `make` to build auto-generated files.

Encourage a run of `make` to build auto-generated files.

Fixes Ben's "unintuitive test procedure" bug:

Date: Wed, 27 Jan 2010 14:09:14 +1100
From: Ben Finney
Subject: [Be-devel] Re: Test suite on Trevor's development branch
...
> $ python ./test.py
> Traceback (most recent call last):
[...]
> ImportError: No module named _version

So it's not possible to simply get a copy of the branch and try running
the test suite.
...