DConf load command requires a slash at the end of the path to load,
but the replace_variables() code always removed the trailing slash,
which made the configuration load nonfunctional.
Store the Evolution version used to create the backup file in the
evolution.dir file which is part of the tarball.
After restoring the backup file we need to reset the last-used-version
key in GSettings to the version listed in the evolution.dir file so the
proper migration routines run when Evolution is restarted.
