Merge recent vendor changes and sync code:

Merge recent vendor changes and sync code:
1862 incremental zfs receive fails for sparse file > 8PB
3112 ztest does not honor ZFS_DEBUG
3122 zfs destroy filesystem should prefetch blocks
3129 'zpool reopen' restarts resilvers
3130 ztest failure: Assertion failed:
       0 == dmu_objset_destroy(name, B_FALSE) (0x0 == 0x10)

References:
  https://www.illumos.org/issues/1862
  https://www.illumos.org/issues/3112
  https://www.illumos.org/issues/3122
  https://www.illumos.org/issues/3129
  https://www.illumos.org/issues/3130

Obtained from:	illumos (vendor/illumos, vendor/illumos-sys)
MFC after:	2 weeks