3195 mpt_sas IOC reset races can cause panics
Reviewed by: Dan McDonald <danmcd@nexenta.com>
Reviewed by: Keith Wesolowski <keith.wesolowski@joyent.com>
Approved by: Garrett D'Amore <garrett.damore@gmail.com>
4171 clean up spa_feature_*() interfaces
4172 implement extensible_dataset feature for use by other zpool features
Reviewed by: Max Grossman <max.grossman@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Approved by: Garrett D'Amore <garrett@damore.org>
	[illumos-gate merge]

commit 2acef22db7808606888f8f92715629ff3ba555b9
    4171 clean up spa_feature_*() interfaces
    4172 implement extensible_dataset feature for use by other zpool features
commit 018d3f06fe63d3b8316ef73502fb8f2dd473ffd1
    3195 mpt_sas IOC reset races can cause panics

Conflicts:
	usr/src/common/zfs/zfeature_common.h (preserve FS_SS_LIMIT)