new extension: fetch -> combine pull and merge/update pull changes from remote repo. if changes add new head: merge with new head, commit result. else: update working dir to new head. this makes useful command like git 'pull' command.

#header#
# HG changeset patch
# User #author#
# Date #date|hgdate#
# Node ID #node#
#parent%changesetparent#
#desc#

#diff#