Factor doupdate into _lookup + hg.update

Fix extensions for merge change

Update mq to use new logmessage arglist from 2794:bd8a9a94139f

Merge with crew

fetch: add missing import.

fetch: do not fetch if working dir modified

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.

commands.logmessage: simplify calling.

localrepo.update: allow to suppress commit reminder.

mq: unused variables, improper usage of 'is [not]', undefined variable

mq: codingstyle

mq: remove unecessary test