* Use I18n.locale instead of ":en"
* Reset I18n.locale value after locale changing tests

* Add locale spec with failing locale plus region check

* Use a more accurate locale when supplied by browser headers

Previously we were using a matching option which would use the first locale
available which matched the locale portion, even if a region was specified.

This changes to first try to find an exact match, and then fall back to the
region, and then fall back to the  default.

* Clean up default_locale method