wireproto: extract repo filtering to standalone function

As part of teaching Mozilla's replication extension to better handle
repositories with obsolescence data, I encountered a few scenarios
where I wanted built-in wire protocol commands from replication clients
to operate on unfiltered repositories so they could have access to
obsolete changesets.

While the undocumented "web.view" config option provides a mechanism
to choose what filter/view hgweb operates on, this doesn't apply
to wire protocol commands because wireproto.dispatch() is always
operating on the "served" repo.

This patch extracts the line for obtaining the repo that
wireproto commands operate on to its own function so extensions
can monkeypatch it to e.g. return an unfiltered repo.

I stopped short of exposing a config option because I view the use
case for changing this as a niche feature, best left to the domain
of extensions.

mercurial/wireproto.py

@@ -536,8 +536,17 b' class ooberror(object):'
     def __init__(self, message):
         self.message = message
 
+def getdispatchrepo(repo, proto, command):
+    """Obtain the repo used for processing wire protocol commands.
+
+    The intent of this function is to serve as a monkeypatch point for
+    extensions that need commands to operate on different repo views under
+    specialized circumstances.
+    """
+    return repo.filtered('served')
+
 def dispatch(repo, proto, command):
-    repo = repo.filtered("served")
+    repo = getdispatchrepo(repo, proto, command)
     func, spec = commands[command]
     args = proto.getargs(spec)
     return func(repo, proto, *args)