wireprotoserver: py3 helpfully calls adds HTTP_ to CONTENT_LENGTH

Just handle both with a membership check, preferring the HTTP_
namespaced version. Sigh.

Differential Revision: https://phab.mercurial-scm.org/D2310

mercurial/wireprotoserver.py

@@ -142,6 +142,9 b' class httpv1protocolhandler(baseprotocol'
         return args
 
     def forwardpayload(self, fp):
+        if r'HTTP_CONTENT_LENGTH' in self._req.env:
+            length = int(self._req.env[r'HTTP_CONTENT_LENGTH'])
+        else:
         length = int(self._req.env[r'CONTENT_LENGTH'])
         # If httppostargs is used, we need to read Content-Length
         # minus the amount that was consumed by args.