libglusterfs: add glusterfs-acl.h to Makefile.am

Without this, glusterfs-acl.h is left out of 'make dist'
and building RPM fails.

Change-Id: I5dc9dc8eecdea4c4c0d06f0b3da23bd2df4e944e
Signed-off-by: Anand Avati <avati@redhat.com>
BUG: 1009210
Reviewed-on: http://review.gluster.org/6015
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>