libglusterfs/client_t client_t implementation, phase 1

Implementation of client_t

The feature page for client_t is at
http://www.gluster.org/community/documentation/index.php/Planning34/client_t

In addition to adding libglusterfs/client_t.[ch] it also extracts/moves
the locktable functionality from xlators/protocol/server to libglusterfs,
where it is used; thus it may now be shared by other xlators too.

This patch is large as it is. Hooking up the state dump is left to do
in phase 2 of this patch set.

(N.B. this change/patch-set supercedes previous change 3689, which was
corrupted during a rebase. That change will be abandoned.)

BUG: 849630
Change-Id: I1433743190630a6d8119a72b81439c0c4c990340
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/3957
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>