Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

truncate(1): Update tests' golden output

After commit 5ee2c35751ef truncate(1)'s usage output was extended.
Update the golden output in test cases to match the changes made.

Sponsored by: The FreeBSD Foundation
Reviewed by: lwhsu
Differential Revision: https://reviews.freebsd.org/D31628

truncate: Add support for -s % and /

% round up to the multiple size and / round down
This is compatible with gnu truncate.
Add tests and document in the man page.

Fix usr.bin.truncate.truncate_test.bad_truncate with ZFS /tmp.

The bad_truncate test sets the uimmutable flag to produce an error in
truncate, but that flag isn't supported by ZFS. If /tmp is on a ZFS
filesystem, the test will fail. Change it to use readonly permissions and
an unpriveleged user instead.

Reviewed by: jilles
MFC after: 1 week
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D4862

truncate: Detect integer overflow, fix relative sizes, add tests.

The change to expand_number (r204654) broke detection of too large sizes and
relative sizes ('+'/'-').

Also add some tests.

PR: 190735
Submitted by: Kirk Russell
MFC after: 1 week