It was an extension just because there were several dependency cycles I
needed to address.
I don't add 'chgserver' to extensions._builtin since chgserver is considered
an internal extension so nobody should enable it by their config.
This is necessary to solve future dependency cycle between commandserver.py
and chgserver.py.
'cmd' prefix is added to table and function names to avoid conflicts with
hgweb.
And call it runservice() because I'll soon add createservice().
The main reason I'm going to introduce the 'server' module is to solve
future dependency cycle between chgserver.py and commandserver.py.
The 'server' module sits at the same layer as the cmdutil. I believe it's
generally good to get rid of things from the big cmdutil module.
