[1.8.x] Fixed #25051 -- Clarified return type of {% now %} tag.

You can also use the syntax ``{% now "Y" as current_year %}`` to store the

output inside a variable. This is useful if you want to use ``{% now %}``

inside a template tag like :ttag:`blocktrans` for example::

output (as a string) inside a variable. This is useful if you want to use

``{% now %}`` inside a template tag like :ttag:`blocktrans` for example::

    {% now "Y" as current_year %}

    {% blocktrans %}Copyright {{ current_year }}{% endblocktrans %}