GSettings migration: only write database on actual changes
GSettings migration: only write database on actual changes

The database was being rewritten in all cases of timestamp changes on
the migration scripts directory -- possibly even if a script had been
removed since last run (or other reasons).

Only rewrite the file if a new migration has actually been run.

hyperair/gconf-gdbus,GNOME/gconf,GNOME/gconf,GNOME/gconf,hyperair/gconf-gdbus,GNOME/gconf,hyperair/gconf-gdbus,hyperair/gconf-gdbus