Renamed unreleased new script, check_dir_perms.sh -> check_dir_ownership.sh.
Fixed exit code in this new script.
Modified p4d_base to call this script as a preflight check when starting p4d
(regular start only, not force_start). It will refuse to start p4d if there
are any files in P4ROOT owned by a user other than the defined OSUSER. This
should be helpful in finding things like a root-owned state.xu file.