httppeer: improve protocol check

Pre-0.6c hgweb used text/plain for protocol responses. This meant
that a web server could serve a static file and confuse a client into
generating a nasty traceback.

Now we insist that text/plain protocol responses not include a
Content-Length, which older hgweb didn't generate but will typically
be produced for static files.

mercurial/httppeer.py

@@ -145,7 +145,8 b' class httppeer(wireproto.wirepeer):'
             raise error.OutOfBandError(resp.read())
         # accept old "text/plain" and "application/hg-changegroup" for now
         if not (proto.startswith('application/mercurial-') or
-                proto.startswith('text/plain') or
+                (proto.startswith('text/plain')
+                 and not resp.headers.get('content-length')) or
                 proto.startswith('application/hg-changegroup')):
             self.ui.debug("requested URL: '%s'\n" % util.hidepassword(cu))
             raise error.RepoError(