Now requires pylibmc.

This method is meant to be used for auxiliary authentication for
privileged operations where the user is asked for his current
password (like a password change).

Whitelisting source IPs now works properly.

Also adds a test for server.py, to verify that the program will
actually start the HTTP server.

gevent.lock is not present in the 0.13.6 gevent release, which is
what is in Debian wheezy.

Also fix the tests so that they run properly (using the right gevent
helpers).

nginx-mail-mapper did the same, which should be enough to make password with %
work, note however that nginx escapes only " " and "%" in this case
(function ngx_escape_uri)