Remove $FreeBSD$: two-line nroff pattern

Remove /^\.\\"\n\.\\"\s*\$FreeBSD\$$\n/

protect.1: Document that protect(1) does not work in jails

The reason is that in order to protect a process procctl(2) needs
the PRIV_VM_MADV_PROTECT privilege, which is currently denied in jails
(see kern_jail.c).

MFC after: 1 week

protect.1: Improve synopsis

While here, make the list's -width argument a bit shorter for
readability.

MFC after: 3 days

protect(1): Correct typo and add newline

Fix a typo, and move a sentence onto a new line in accordance with
mdoc(7) syntax.

While here, also remember to bump .Dd accordingly, as it was missed in
the prior commit.

Reported by: maxim@

protect.1: document existence of _oomprotect

Improve discoverability of the functionality by mentioning in the
userland tool manual. Add a SEE ALSO entry to rc.conf(5) where more
details are provided.

Sponsored by: Fudo Security (a.wolk)
Differential Revision: https://reviews.freebsd.org/D30334

Reassign copyright statements on several files from Advanced
Computing Technologies LLC to Hudson River Trading LLC.

Approved by: Hudson River Trading LLC (who owns ACT LLC)
MFC after: 1 week

Correct stale comments.

Approved by: re (joel)

Minor mdoc improvements.

Approved by: re (blanket)

Extend the support for exempting processes from being killed when swap is
exhausted.
- Add a new protect(1) command that can be used to set or revoke protection
from arbitrary processes. Similar to ktrace it can apply a change to all
existing descendants of a process as well as future descendants.
- Add a new procctl(2) system call that provides a generic interface for
control operations on processes (as opposed to the debugger-specific
operations provided by ptrace(2)). procctl(2) uses a combination of
idtype_t and an id to identify the set of processes on which to operate
similar to wait6().
- Add a PROC_SPROTECT control operation to manage the protection status
of a set of processes. MADV_PROTECT still works for backwards
compatability.
- Add a p_flag2 to struct proc (and a corresponding ki_flag2 to kinfo_proc)
the first bit of which is used to track if P_PROTECT should be inherited
by new child processes.

Reviewed by: kib, jilles (earlier version)
Approved by: re (delphij)
MFC after: 1 month