Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r268238:

Add an option, -p, which makes gstat(8) to only display physical providers
(those with rank of 1).

MFC r266320:
Add -o option to gstat to display "other" operatins (e.g. BIO_FLUSH).

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

o Turn the batch mode on if stdout is not tty.

Submitted by: vsevolod
MFC after: 1 week

o Sync synopsis with reality. Remove BUG section -- there is
a batch mode in gpart(8) now.

- Allow gstat to print values to different kind of outputs.
- Introduce batch mode, where gstat will collect the numbers, print them, and
exit.
- Document batch mode in the gstat man page.

Submitted by: anders

Language tweak.

- Add support for filtering the the list of providers by a regular
expression, which makes it possible to only see interesting
providers. "f" is used inside gstat to set a filter, "F" is used to
remove current filter.
- Do not print some uninteresting values in the gstat title line.
- Do not print past the end of the screen.
- Read multiple keystrokes per "wait" when gstat is running.
- Remove a redundant != check, right after check of NULL against the
same variable ("gid").
- Use sysexits.h.
- Do not link against libkvm and libsbuf, they are not actually used.
- Fix a few style(9) issues where I had to touch nearby code anyway.

Approved by: cperciva (mentor)
MFC after: 2 weeks

Add cross-references to iostat, systat and vmstat.

Added the EXIT STATUS section where appropriate.

Add an '-a' switch to only display providers that are at least
0.1% busy.

OK'ed by: phk

Markup nits.

Add -d flag to monitor BIO_DELETE operations too

Sigh, I guess this manpage used cat(1) as a template?

Otherwise, fix the manpage to not use the second person,
and add two missing punctuation bits.

Add a small manpage.