tests: make test-hgweb.t output stable

Instability introduced in combination of a4d7fd7ad1f7 and e389a25e7e60.

tests/get-with-headers.py

@@ -32,7 +32,8 b' def request(host, path, show):'
     response = conn.getresponse()
     print response.status, reasons.get(response.reason, response.reason)
     if show[:1] == ['-']:
-        show = [h for h, v in response.getheaders() if h.lower() not in show]
+        show = sorted(h for h, v in response.getheaders()
+                      if h.lower() not in show)
     for h in [h.lower() for h in show]:
         if response.getheader(h, None) is not None:
             print "%s: %s" % (h, response.getheader(h))