include <limits.h> for PATH_MAX

I need to include <limits.h> in order to use PATH_MAX, Otherwise it will
not build at mine. I believe it is standard compliant to do so:
http://pubs.opengroup.org/onlinepubs/009695399/basedefs/limits.h.html

BUG: 764655
Change-Id: I3f124466f7f7742e94a9d1256bc9239ec16aab04
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/5340
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>