[RHEL/6] audit_mac_changes rule:
* Unify XCCDF ID with OVAL ID (in XCCDF & profile references),
* Fix OVAL check:
  - allow 'aw' together with 'wa' in access mode specification
  - also make [aw|wa] minimum requirement, not the exact one
    (IOW allow also stronger audit masks like 'raxw'),
* Add RHEL-6 remediation script.