RFC: allow "hg merge" to take a URL argument, add autocommit option

[Gil]

Bryan O'Sullivan wrote:
> If given no arguments, or given a revision ID (or tag, or what have
> you), it behaves exactly as it does now.
> 
> If given a URL as an argument, it pulls changes from that URL, and
> either updates the working dir if there have been no heads added, does a
> merge if there is one added head, and does no merge or update (but
> prints a message saying why) if there are more than one added heads.

This would make the new merge different from pull in that it won't
honor the default pull configuration in your hgrc.  Don't most
people arrange for upstream to be the default?

hg pull
hg merge
hg commit

I find that I'll do almost anything to not have to remember to type
a URL for upstream.

--Gil