Do not hide traceback with failures from --fail-on-template-vars

Ref: #222 (comment)

Author: blueyed

pytest_django/plugin.py

@@ -573,7 +573,7 @@ def __mod__(self, var):
             else:
                 msg = "Undefined template variable '%s'" % var
             if self.fail:
-                pytest.fail(msg, pytrace=False)
+                pytest.fail(msg)
             else:
                 return msg
 

tests/test_environment.py

@@ -97,7 +97,7 @@ def test_ignore(client):
         origin = "'invalid_template.html'"
     result.stdout.fnmatch_lines_random([
         "tpkg/test_the_test.py F.",
-        "Undefined template variable 'invalid_var' in {}".format(origin)
+        "E * Failed: Undefined template variable 'invalid_var' in {}".format(origin)
     ])