Implemented auto-escaping of variable output in templates. Fully controllable...

Implemented auto-escaping of variable output in templates. Fully controllable by template authors and it's possible to write filters and templates that simulataneously work in both auto-escaped and non-auto-escaped environments if you need to. Fixed #2359

See documentation in templates.txt and templates_python.txt for how everything
works.

Backwards incompatible if you're inserting raw HTML output via template variables.

Based on an original design from Simon Willison and with debugging help from Michael Radziej.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6671 bcc190cf-cafb-0310-a4f2-bffc1f526a37