Prevent races running the queue by serializing access to the
queue directory.

PR:		bin/113239
Add the name of the file that could not be opened to the error message
regarding the failure.

Suggested while working on PR bin/113239.
MFV r251619:

ZFS needs better comments.

Illumos ZFS issues:
  3741 zfs needs better comments

MFC after:      2 weeks
Bump the CPU/WCPU column width by one so that it fits values from 100% up
to 999.99% CPU.  It still won't be aligned if you have a multithreaded
process using more than 1000% CPU (e.g. idle process on an idle 12-way
system), but 100% is a common case.

Submitted by:	Jeremy Chadwick (partial)
MFC after:	1 week
MFV r251620:

ZFS comments need cleaner, more consistent style

Illumos ZFS issues:
  3741 zfs comments need cleaner, more consistent style

MFC after:      2 weeks
MFV r251621:

ZFS needs a refcount audit

Illumos ZFS issues:
  3741 zfs needs a refcount audit

MFC after:      2 weeks
MFV r251622:

ZFS shouldn't ignore errors unmounting snapshots

Illumos ZFS issues:
  3744 zfs shouldn't ignore errors unmounting snapshots

MFC after:      2 weeks