rewrite: use cmdutil.logmessage instead of ad-hoc methods
The logic for handling the --message and --logfile options is already
in core hg in the cmdutil.logmessage function. This patch removes this
duplicate logic from Evolve and just calls the core function.
fold: enable --date and --user options
Like all other commit-creating commits, `hg fold` should also have
these options enabled. This also allows getting consistent hashes
during tests involving fold.