New options: --owner-map and --group-map.

New options: --owner-map and --group-map.

* NEWS: Update.
* doc/tar.1: Document --owner-map and --group-map
* doc/tar.texi: Likewise.

* src/map.c: New file.
* src/Makefile.am: Add map.c
* src/common.h (owner_map_read, owner_map_translate)
(group_map_read, group_map_translate): New protos.
* src/create.c (start_header): Use owner_map_translate
and group_map_translate to optionally translate user/group names/ids.
* src/tar.c: New options --owner-map and --group-map.

* tests/map.at: New file.
* tests/Makefile.am: Add map.at
* tests/testsuite.at: Include map.at.