Returns the current priority for a process, a process group, or a user. (See getpriority(2).) Will raise a fatal exception if used on a machine that doesn't implement getpriority(2).
WHICH can be any of PRIO_PROCESS, PRIO_PGRP or PRIO_USER imported from "RESOURCE CONSTANTS" in POSIX.
Portability issues: "getpriority" in perlport.