wireprotoserver: return to using iscmd() method

This was teased out in part so remotefilelog could disable an old
protocol method over http. It got dropped accidentally in the recent
refactor, but the code was all still present so it's easy to support
for now.

I think once we land remotefilelog, we should probably inline this
function.

Differential Revision: https://phab.mercurial-scm.org/D2285

mercurial/wireprotoserver.py

@@ -170,6 +170,10 b' class httpv1protocolhandler(baseprotocol'
             urlreq.quote(self._req.env.get('REMOTE_HOST', '')),
             urlreq.quote(self._req.env.get('REMOTE_USER', '')))
 
+# This method exists mostly so that extensions like remotefilelog can
+# disable a kludgey legacy method only over http. As of early 2018,
+# there are no other known users, so with any luck we can discard this
+# hook if remotefilelog becomes a first-party extension.
 def iscmd(cmd):
     return cmd in wireproto.commands
 
@@ -198,7 +202,7 b' def parsehttprequest(repo, req, query):'
     # wire protocol requests to hgweb because it prevents hgweb from using
     # known wire protocol commands and it is less confusing for machine
     # clients.
-    if cmd not in wireproto.commands:
+    if not iscmd(cmd):
         return None
 
     proto = httpv1protocolhandler(req, repo.ui)