Add support for preserving ACL entries of files.
* configure.ac (acl): New option.
(HAVE_POSIX_ACL): Test for POSIX ACL support. This is typically
provided by libacl on GNU/Linux.
* fileio.c (Ffile_acl, Fset_file_acl): New functions.
(Fcopy_file): Change last arg to `preserve_extended_attributes'
and copy ACL entries of file in addition to SELinux context if
set.
(syms_of_fileio): Add `file-acl' and `set-file-acl'.
* Makefile.in (LIBACL_LIBS): New macro.
(LIBES): Use it.
* files.el (file-extended-attributes)
(set-file-extended-attributes): New functions.
(backup-buffer): Use them to handle both SELinux context and ACL
entries.
(backup-buffer-copy): Work with an alist of extended attributes,
rather than an SELinux context.
(basic-save-buffer-2): Ditto.
* files.texi (File Attributes): Document ACL support and new
`file-acl' function.
(Changing Files): Mention argument name change of `copy-file' and
document new function `set-file-acl'.