extras/checkpatch.pl: linux kernel style patch verification

This is to bring in adherence to coding policy, prior to patch
submission for review.

 - no tabs
 - no whitespace
 - indentation (linux style) etc.

This is in the interest at large for the GlusterFS codebase
to be more cleaner and readable.

./rfc.sh - now supports running this for all patches diverged
from "origin/master" revision.

NOTE: One should take this as a handle for good guidelines and
never use it as a tool for correctness, use common-sense in all
the cases ;-)

Change-Id: Ib9a5ed207cde152cb92b8d38cec83e8ce9ef7f28
BUG: 1120646
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/8181
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anders Blomdell <anders.blomdell@control.lth.se>