Posix ACL Support (WIP)

Initial Posix ACL support.  This patch build cleanly under Centos 6
which is based on a 2.6.32 kernel.  Once the autoconf tests listed
below are implemented it should work on more modern kernels.

TODO:
* Add autoconf HAVE_GET_ACL check
* Add autoconf HAVE_POSIX_ACL_RELEASE check
* Add autoconf HAVE_INODE_OWNER_OR_CAPABLE check
* Update zfs(8) man page to include acltype section
* Update zfs(8) man page to indicate aclinherit does nothing
* Test, test, test...

Test Summary Report
-------------------
pjd-fstest-20090130-RC/tests/xacl/00.t (Wstat: 0 Tests: 45 Failed: 1)
  Failed test:  45
pjd-fstest-20090130-RC/tests/xacl/02.t (Wstat: 0 Tests: 80 Failed: 16)
  Failed tests:  11, 14, 18, 22, 26, 30, 34, 38, 46, 49
                53, 57, 61, 65, 69, 73
pjd-fstest-20090130-RC/tests/xacl/03.t (Wstat: 0 Tests: 57 Failed: 2)
  Failed tests:  27, 55
Files=7, Tests=330,  4 wallclock secs
Result: FAIL

The xacl/00.t test 45 failure is also observed on ext[234] so this is
most likely a flaw in the test case.  However, all the other test
failures need to be investigated and resolved.  The above results
are from CentOS 6.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #170
Posix ACL Support (WIP)

Rebased on Brian's rework of the code.

TODO:
* zpl_xattr_acl_init() can be simplied.  It should be called from
  either zfs_mknode() or zfs_znode_alloc() prior to the new inode
  being unlocked.

Compile-time tested against 2.6.27-3.11 (except 2.6.28,2.6.36).

To be run-time tested, after rework.

Signed-off-by: Massimo Maggi <me@massimo-maggi.eu>
Merged my autoconf with Brian's improvements