quick fix for 500 errors when sending a HEAD request to deliverance-proxy

deliverance-headrequest.patch

diff --git a/deliverance/middleware.py b/deliverance/middleware.py
index 03c3b70..f44af34 100644
--- a/deliverance/middleware.py
+++ b/deliverance/middleware.py
@@ -101,12 +101,18 @@ class DeliveranceMiddleware(object):
                 return self.clientside_response(req, rule_set, resource_fetcher, log)(environ, start_response)
             else:
                 log.debug(self, 'Not doing clientside theming because jsEnabled cookie not set')
+
+        headresp = None
+        if req.method == "HEAD":
+            headresp = req.get_response(self.app)
+            req.method = "GET"
         resp = req.get_response(self.app)
+
         ## FIXME: also XHTML?
         if resp.content_type != 'text/html':
             ## FIXME: remove from known_html?
             return resp(environ, start_response)
-        
+
         # XXX: Not clear why such responses would have a content type, but
         # they sometimes do (from Zope/Plone, at least) and that then breaks
         # when trying to apply a theme.
@@ -128,8 +134,11 @@ class DeliveranceMiddleware(object):
             resp.body = self._substitute_jsenable(resp.body)
         resp = log.finish_request(req, resp)
 
+        if headresp:
+            headresp.headers = resp.headers
+            resp = headresp
         return resp(environ, start_response)
-
+        
     _title_re = re.compile(r'<title>(.*?)</title>', re.I|re.S)
 
     def _get_title(self, body):