add a standard http response for permanent redirect

[hugo]

HttpResponseRedirect uses 302 as it's status code. That's FOUND, not MOVED PERMANTLY - the latter is 301. For that there is no prebuilt response, but it should be added (because in many cases it is much more appropriate to tell the client to use the new URL and forget about the old one). This little patch adds a 301 status code:

Index: utils/httpwrappers.py
===================================================================
--- utils/httpwrappers.py       (revision 1779)
+++ utils/httpwrappers.py       (working copy)
@@ -212,6 +212,12 @@
         self['Location'] = redirect_to
         self.status_code = 302
 
+class HttpResponsePermanentRedirect(HttpResponse):
+    def __init__(self, redirect_to):
+        HttpResponse.__init__(self)
+        self['Location'] = redirect_to
+        self.status_code = 301
+
 class HttpResponseNotModified(HttpResponse):
     def __init__(self):
         HttpResponse.__init__(self)

Situations where we do fixed redirects - for example those done by the CommonMiddleware - should actually use 301 instead of 302.