Simplify killing processes.

* Do not hook rt_sigaction or signal (32 bit).
* Old "interrupted" logic is unnecessary since parrot-native-fd branch.
* New pfs_process_cankill (formally pfs_process_raise) which encapsulates the
  logic pfs_dispatch*.cc needs for handling the kill system call.
* Remove obsolete logic in decode_write for handling SIGPIPE, which was necessary
  before parrot-native-fd when Parrot handled all tracee pipes.
Exit with an error if an auth method is unknown.

This confused some of our Physics friends because they were using -a=unix which
tries to:

    auth_register_byname("=unix");

which silently failed.
Simplify killing processes.

* ccl/pull/543/head:
  Simplify killing processes.

Conflicts:
	parrot/src/pfs_main.cc
Simple priority submission feature for WQ.
Modified send_one_task to iterate over the ready list, so as to keep tasks in priority order.
Factored push_task_to_ready_list so that all inserts follow the same logic.
Merge changes.