Use factories, not fixtures, in integration spec.

Removes the dependency on fixtures having been loaded.
Allow resetting of the locale pattern on the locale routing filter.

An order-dependent error in locale integration tests
(https://travis-ci.org/mysociety/alaveteli/jobs/37914013) showed that
the routing filter pattern was not being updated from it's initial value
when a new set of available locales was passed to AlaveteliLocalization.
Merge branch 'fix_transient_locale_integration_errors' into rails-3-develop