Add basic suuport for extended attributes.

Add basic suuport for extended attributes.

* src/Makefile.am: Add xattrs.[ch]
* src/xattrs.c: New file.
* src/xattrs.h: New file.
* src/common.h (READ_LIKE_SUBCOMMAND): New define.
(selinux_context_option, acls_option, xattrs_option): New globals.
(xheader_xattr_init, xheader_xattr_free)
(xheader_xattr_copy, xheader_xattr_add): New protos.
(WARN_XATTR_WRITE): New mask.
* src/create.c (start_header): Handle xattrs pairs if in POSIX format.
(dump_file0): Handle extended attributes.
* src/extract.c (delayed_set_stat,delayed_link) <xattr_map_size>
<xattr_map>: New members.
(set_xattr): New static function.
(open_output_file): Accept an additional argument indicating
whether the file has already been created.
(set_stat,delay_set_stat)
(apply_nonancestor_delayed_set_stat)
(extract_file): Handle extended attributes.
* src/list.c (decode_header, simple_print_header): Display
extended attributes.
* src/tar.c: New options --xattrs, --no-xattrs, --xattrs-include,
--xattrs-exclude
(tar_stat_destroy): Free the xattr_map storage.
* src/tar.h (xattr_array): New struct.
(tar_stat_info) <xattr_map_size, xattr_map>: New members.
* src/warning.c: New warning control keyword "xattr-write".
* src/xheader.c (xheader_xattr_init)
(xheader_xattr_free, xheader_xattr_add)
(xheader_xattr_copy): New functions.
(struct xhdr_tab) <prefix>: New member.
(locate_handler): Permit selecting the keyword based on its
prefix.
(xheader_protected_pattern_p)
(xheader_protected_keyword_p): Likewise.
(xattr_coder, xattr_decoder): New functions.
(xhdr_tab): Reflect the changes to struct xhdr_tab.
New keyword "SCHILY.xattr".
* tests/Makefile.am: Add new tests.
* tests/testsuite.at: Likewise.
(AT_CHECK_UTIL, AT_XATTRS_UTILS_PREREQ)
(AT_CAPABILITIES_UTILS_PREREQ, AT_XATTRS_PREREQ): New defuns.
* tests/xattr01.at: New test.
* tests/xattr02.at: New test.
* tests/xattr03.at: New test.
* tests/xattr04.at: New test.
* tests/capabs_raw01.at: New test.