Negligible formatting changes to django/template/__init__.py -- fixed some spacing issues, renamed NotImplemented to NotImplementedError and changed some 'raise' statements to use callable exceptions instead of the old-style comma technique

git-svn-id: http://code.djangoproject.com/svn/django/trunk@6971 bcc190cf-cafb-0310-a4f2-bffc1f526a37