Cleaned up the template debug implementation.

This patch does three major things:

* Merges the django.template.debug implementation into django.template.base.

* Simplifies the debug implementation.

  The old implementation copied debug information to every token and node.
  The django_template_source attribute was set in multiple places, some
  quite hacky, like django.template.defaulttags.ForNode.

  Debug information is now annotated in two high-level places:

  * Template.compile_nodelist for errors during parsing
  * Node.render_annotated for errors during rendering

  These were chosen because they have access to the template and context
  as well as to all exceptions that happen during either the parse or
  render phase.

* Moves the contextual line traceback information creation from
  django.views.debug into django.template.base.Template. The debug views now
  only deal with the presentation of the debug information.

tests/template_tests/test_parser.py

@@ -5,11 +5,10 @@ from __future__ import unicode_literals
 
 from unittest import TestCase
 
-from django.template import Library, Template, TemplateSyntaxError
+from django.template import Library, TemplateSyntaxError
 from django.template.base import (
     TOKEN_BLOCK, FilterExpression, Parser, Token, Variable,
 )
-from django.test import override_settings
 from django.utils import six
 
 
@@ -73,14 +72,6 @@ class ParserTests(TestCase):
         with six.assertRaisesRegex(self, TypeError, "Variable must be a string or number, got <(class|type) 'dict'>"):
             Variable({})
 
-    @override_settings(DEBUG=True)
-    def test_compile_filter_error(self):
-        # regression test for #19819
-        msg = "Could not parse the remainder: '@bar' from 'foo@bar'"
-        with six.assertRaisesRegex(self, TemplateSyntaxError, msg) as cm:
-            Template("{% if 1 %}{{ foo@bar }}{% endif %}")
-        self.assertEqual(cm.exception.django_template_source[1], (10, 23))
-
     def test_filter_args_count(self):
         p = Parser("")
         l = Library()