Removed custom WSGIRequestHandler.get_environ

We probably historically customized it for good reasons, but
currently, the differences with upstream Python are not
significant any longer.
Also fixes #19075 for which a test has been added.

tests/regressiontests/servers/urls.py

@@ -9,4 +9,5 @@ urlpatterns = patterns('',
     url(r'^example_view/$', views.example_view),
     url(r'^model_view/$', views.model_view),
     url(r'^create_model_instance/$', views.create_model_instance),
-)
+    url(r'^environ_view/$', views.environ_view),
+)