Fixed #10545 -- Mentioned that template context variables are scoped to the...

Fixed #10545 -- Mentioned that template context variables are scoped to the block in which they're assigned. Thanks to yaniv.haber for the report and timo for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14350 bcc190cf-cafb-0310-a4f2-bffc1f526a37