Fixed #892 -- TemplateDoesNotExist errors now get a 'Template-loader...

Fixed #892 -- TemplateDoesNotExist errors now get a 'Template-loader postmortem' section on the pretty debug page. Thanks for the idea, David Ascher

git-svn-id: http://code.djangoproject.com/svn/django/trunk@1400 bcc190cf-cafb-0310-a4f2-bffc1f526a37