LU-1331 changelog: allow changelog to extend record

LU-1331 changelog: allow changelog to extend record

Previously rename is split into two records, this isn't natural and
makes replication hard because rename needs two records, but they
may not be consecutive.

To solve this, allow Changelog to extend record, add fields sfid/spfid
in changelog record to store source/parent fid, and pack both source
and target name into the record.

Added changelog flag CLF_RENAME_LAST: rename unlink of last hardlink
of the target.

Added macro HAVE_CHANGELOG_EXTEND_REC: liblustreapi receives all
changelog records in changelog_ext_rec format.

Signed-off-by: Lai Siyao <laisiyao@whamcloud.com>
Change-Id: I97b990687726e45e661cfb11609f80132c84825d
Reviewed-on: http://review.whamcloud.com/2577
Tested-by: Hudson
Reviewed-by: Thomas LEIBOVICI - CEA <thomas.leibovici@cea.fr>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>