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.

#!/bin/sh

hg init a
echo a > a/a
hg --cwd a ci -A -m a
hg clone a b
echo b > b/b
hg --cwd b ci -A -m b
chmod 100 a/.hg
hg --cwd b push ../a
chmod 700 a/.hg