features: add a directory-protection translator

This is useful to find all calls that remove a file from the protected
directory, including renames and internal calls.  Such calls will cause
a stack trace to be logged.  There's a filter script to add the needed
translators, and then the new functionality can be invoked with one of
the following commands.

	setfattr -n trusted.glusterfs.protect -v log $dir
	setfattr -n trusted.glusterfs.protect -v reject $dir
	setfattr -n trusted.glusterfs.protect -v anything_else $dir

The first logs calls, but still allows them.  The second rejects them
with EPERM.  The third turns off protection for that directory.

Change-Id: Iee4baaf8e837106be2b4099542cb7dcaae40428c
BUG: 888072
Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-on: http://review.gluster.org/4496
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>