Fixed #5133 -- Explicitly close memcached connections after each request

(similar to database connection management). We can't effectively manage the
lifecycle by pooling connections and recent versions of python-memcache can
lead to connection exhaustion in some quite reasonable setups.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8418 bcc190cf-cafb-0310-a4f2-bffc1f526a37