Fixed #2026 -- Added support for 'and' in template 'if' tags, added dozens of...

Fixed #2026 -- Added support for 'and' in template 'if' tags, added dozens of unit tests and updated docs. Thanks, ckknight

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3108 bcc190cf-cafb-0310-a4f2-bffc1f526a37