* gnulib.modules: Add closeout, exitfial.

* gnulib.modules: Add closeout, exitfial.
* lib/.cvsignore: Add __fpending.c, __fpending.h, closeout.c,
closeout.h.
* src/buffer.c: Incluse closeout.h.
(_open_archive): Use freopen rather than fopen, so
that stdlis is always either stdout or stderr.  Use
close_stdout_set_file_name to report its name.
* src/tar.c: Include closeout.h and exitfail.h.
(parse_opt, usage): Call close_stdout as appropriate, to check for
write errors.
(decode_options): Exit with status TAREXIT_FAILURE, not 1.
(main): Set exit_failure, to exit with proper status on memory
allocation failure and the like.
Use close_stdout rather than rolling our own test.