evolve: abort when trying to move a node on top of itself
This provides a clearer error message when evolve misstakenly tries
to move a changeset on top of itself. Before we got an abort with a
cryptic message about trying to rebase a merge changeset.
A proper fix to make sure that evolve never tries to move a node on
top of itself will come in later patches.
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.