Run with show source so we can see the context in travis errors. Add stats for
number of errors. And limit ourselves to mopidy and tests as I happen to have
a tmp folder with non-conforming proof of concept code that I don't want this
to check.
This allows for testing across multiple environments, including Python 3 in
the not too distant future. The instant bonus is that this allows for testing
the docs build at Travis so I don't make more releases like 0.18.2 with broken
docs.
Testing across Python 2.6 and 2.7 with tox is no longer working on systems
which doesn't ship both Python versions by default. I can install Python 2.6 on
a newer Ubuntu system using the deadsnakes PPA, but dependencies installed from
APT, like gobject and gstreamer are still only installed for Python 2.7, thus
making tox useless.
