Log conflicts separately

This patch makes commands that produce a conflict log that final
conflicting push separately from the rest of the command's effects.
This makes it possible for the user to roll back just the final
conflicting push if she desires. (Rolling back the whole operation is
of course still possible, by resetting to the state yet another step
back in the log.)

This change only applies to the new-infrastructure commands.

Signed-off-by: Karl Hasselström <kha@treskal.com>