acls: bugfix for default ACLs extraction

When --acls option is on (regardless of tarball contents or
tarball format), we should explicitly set OR delete default ACLs
for extracted directories.  Prior to this update, we always
created arbitrary default ACLs based standard file permissions.

* configure.ac (with_posix_acls): Check also for acl_free and
acl_delete_def_file to mark IEEE 1003.1e ACLs as supported.
* src/xattrs.c (acl_delete_def_file_at): New function.
(xattrs__acls_set): Do not treat acls_option at all;  Delete
default ACLs if appropriate.

References:
http://www.mail-archive.com/bug-tar@gnu.org/msg04355.html
Thanks: Juan J. Martínez and Mark Steinborn