zfsboottest: sync with changes in zfs boot code

- spa status can not be called before spa init
- libzfs.h inclusion is now required
- fix alternative code for explicit root dataset lookup

MFC after:	10 days
zfsboottest.sh: remove checks for things that are not strictly required

MFC after:	10 days
Add one more ID of Marvell SATA controller.

Submitted by:	marck
MFC after:	3 days
zfs: load zpool.cache after a root fs is mounted

MFC after:	3 weeks
default loader.conf: there is no need to load zpool.cache now

kernel does not need it for importing a root pool.

MFC after:	4 weeks
amd64: use -mno-omit-leaf-frame-pointer in addition to -fno-omit-frame-pointer

... in kernel builds.  This is to make behavior of clang consistent with
behavior of gcc.

MFC after:	2 weeks
zfs: try to properly handle i/o errors in mappedread_sf

Unconditionally freeing a page is not good, especially if it is the page
that was wired by the caller.  The checks are picked up from
kern_sendfile.

MFC after:	3 weeks
Add ID for Marvell 88SE9215 AHCI SATA controller.

MFC after:	3 days
namecache sdt: freebsd doesn't support structured characters yet

:-)

MFC after:	 7 days
rc.d/zfs: pass -v option to zfs mount

this should make boot process more informative (and entertaining)
on systems with lots of zfs filesystems.

MFC after:	7 days
should_yield: protect from td_swvoltick being uninitialized or too stale

The distance between ticks and td_swvoltick should be calculated as
an unsigned number.  Previously we could end up comparing a negative
number with hogticks in which case should_yield() would give incorrect
answer.

We should probably ensure that td_swvoltick is properly initialized.

Sponsored by:	HybridCluster
MFC after:	5 days
audit_proc_coredump: check return value of audit_new

audit_new may return NULL if audit is disabled or suspended.

Sponsored by:	HybridCluster
MFC after:	7 days
dtrace/fasttrap: install hook functions only after all data is
initialized

Sponsored by:	HybridCluster
MFC after:	 7 days