Added translation.override() context manager to docs.

For example::

    from django.utils import translation

    def welcome_translated(language):

        cur_language = translation.get_language()

        try:

for the current thread, and ``django.utils.translation.check_for_language()``

which checks if the given language is supported by Django.

To help write more concise code, there is also a context manager

``django.utils.translation.override()`` that stores the current language on

enter and restores it on exit. With it, the above example becomes::

    from django.utils import tranlations

    def welcome_translated(language):

        with translation.override(language):

            return translation.ugettext('welcome')

Language cookie

---------------