Zap ez_setup dependency.

Use ez_setup only if setuptools can't be imported. Don't depend on it, as
setuptools is only required during packaging/installation, not runtime.
Drop the execute bit on our py files.

(Splitting up a patch originally by @tseaver.)
Switch to tox for testing.

This drops the fixed copy of mox, and adds a `tox.ini`. Still doesn't work.
Get some tests passing in tox.

Filters the `tox` test command down to a whitelist for now, and disables one
test that needs investigation.
Turn on travis.