Fixed #603 -- Added template debugging errors to pretty error-page output, if...

Fixed #603 -- Added template debugging errors to pretty error-page output, if TEMPLATE_DEBUG setting is True. Also refactored FilterParser for a significant speed increase and changed the template_loader interface so that it returns information about the loader. Taken from new-admin. Thanks rjwittams and crew

git-svn-id: http://code.djangoproject.com/svn/django/trunk@1379 bcc190cf-cafb-0310-a4f2-bffc1f526a37