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

Similar commit in main:
(cherry picked from commit b2c76c41be32)

EINTEGRITY was previously documented as a UFS-specific error for
mount(2).  This documents EINTEGRITY as a filesystem-independent error
that may be reported by the backing store of a filesystem.

While here, document EIO as a filesystem-independent error for both
mount(2) and posix_fadvise(2).  EIO was previously only documented for
UFS for mount(2).

Reviewed by:	mckusick
Suggested by:	mckusick
MFC after:	2 weeks
Sponsored by:	Chelsio Communications
Differential Revision:	https://reviews.freebsd.org/D24168

Update the man page to mention that extending a file with truncate(2)
is required by POSIX as of 2008.

Reviewed by:	bcr
MFC after:	2 weeks
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D23354

Renumber cluase 4 to 3, per what everybody else did when BSD granted
them permission to remove clause 3. My insistance on keeping the same
numbering for legal reasons is too pedantic, so give up on that point.

Submitted by:	Jan Schaumann <jschauma@stevens.edu>
Pull Request:	https://github.com/freebsd/freebsd/pull/96

- Note that ftruncate(2) can operate on shared memory objects and cross
  reference shm_open(2).
- Note that ftruncate(2) does not change the file position pointer (aka
  seek pointer) of the file descriptor.
- ftruncate(2) will fail with EINVAL for all sorts of other fd types than
  just sockets, so instead note that it fails for all but regular files and
  shared memory objects.
- Note that ftruncate(2) also appeared in 4.2BSD along with truncate(2).
  (Or at least the manpage for both appeared in 4.2, I did not check the
  kernel code itself to see if either predated 4.2.)

PR:		199472 (2)
Submitted by:	andrew@ugh.net.au (2)
MFC after:	1 week

clause.

# If I've done so improperly on a file, please let me know.

  maximum file size.
- truncate(2) returns EINVAL if the length argument was less than 0.

and ftruncate(2) return EPERM.

Note, that if the append-only flag is set even increasing size of the file
is not permitted.

Submitted by:	ceri