The locale is a global state, and it was not properly reset to
whatever it was before the unitttest possibly changed it.
This is now fixed.
Not restoring the locale led to weird issues: depending on
the order chosen by "python -m unittest discover" to run
the unit tests, some tests would apparently randomly fail
due to the locale not being what was expected.
For example, test_period_in_timeperiod_archive would
call mock('posts/1970/ 1月/index.html',...) instead of
expected mock('posts/1970/Jan/index.html',...) and fail.
PAGINATION_PATTERNS was hard coded so that all files had a ".html" extension. This fixes that and add a test to
ensure that the pagination code is not changing the filename incorrectly.
