Fix up POSIX permission handling

Fix up POSIX permission handling

	* fhandler_disk_file.cc (fhandler_disk_file::fchmod): Disable
	deviation from POSIX 1003.1e in terms of GROUP_OBJ/CLASS_OBJ
	permissions.  Follow POSIX 1003.1e again.  Keep old code in
	for future reference.
	* sec_acl.cc: Accommodate changes in ACE creation in leading
	comment.
	(set_posix_access): Fix user deny ACE creation.  Split group
	deny ACE creation into two steps, one to reflect CLASS_OBJ,
	the other to reflect OTHER_OBJ.