evolve: fix the conflicts error message during content-divergence resolution
Before last patch, we didn't had an automated way to continue an interrupted
content-divergence resolution and we used to show a very long error message on
how to continue manually.
This patch replaces that long error message with nice small message which tells
how to continue and how to abort. We still show `hg update -C .` to abort as we
need to test and make `--abort` work in case of content-divergence.