Fix bug #68526 Implement POSIX Access Control List for UDS

- add --with-fpm-acl build option which allow to manage ACL
on Unix Domain Socket
- add listen.acl_users pool option
- add listen.acl_groups pool option

Keep old behavior (chmod) if option not used or not supported.
NEWS
Merge branch 'PHP-5.6'

* PHP-5.6:
  NEWS
  Fix bug #68526 Implement POSIX Access Control List for UDS