Use the updated repository upgrade API.
Use the updated repository upgrade API.

* subversion/svnadmin/main.c
  (repos_notify_handler): Add the notification for starting an upgrade.
  (upgrade_started): Remove.
  (subcommand_upgrade): Use the new API, and the notification system.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion