Illumos #3561, #3116

Illumos #3561, #3116

3561 arc_meta_limit should be exposed via kstats
3116 zpool reguid may log negative guids to internal SPA history
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Gordon Ross <gordon.ross@nexenta.com>
Approved by: Garrett D'Amore <garrett@damore.org>

References:
  https://www.illumos.org/issues/3561
  https://www.illumos.org/issues/3116
  illumos/illumos-gate@20128a0826f9c53167caa9215c12f08beee48e30

Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Porting Notes:

1. The spa change was accidentally included in the libzfs_core merge.

2. "Add missing arcstats" (1834f2d8b715d25bafbb0e4a099994f45c3211ae)
   already implemented these kstats a few years ago.