* modules/openat (Files): Add lib/openat-die.c.

* modules/openat (Files): Add lib/openat-die.c.
(Depends-on): Remove error, exitfail.
Add dirname.
* lib/openat.c (fdopendir): Be sure to close the supplied
file descriptor before returning.  This makes our replacement
implementation a little closer to Solaris's, where fdopendir
ties the file descriptor to the returned DIR* pointer.
* lib/openat.c (unlinkat): New function.
* lib/openat.h (unlinkat): Add prototype.
* lib/openat-die.c (openat_save_fail): Rename from openat_save_die.
(openat_restore_fail): Rename from openat_restore_die.
* lib/openat.c, openat.h: Reflect s/_die/_fail/ renaming.

Provide an alternative to exiting immediately upon save_cwd or
restore_cwd failure.  Now, an application can arrange e.g.,
to perform a longjump in that case.
* lib/openat.c: Include dirname.h.
Use IS_ABSOLUTE_FILE_NAME rather than testing for leading slash.
(rpl_openat, fdopendir, fstatat): Call openat_save_die
and openat_restore_die rather than calling error directly.
Don't include "error.h" or "exitfail.h"; they're no longer needed.

* lib/openat-die.c (openat_save_die, openat_restore_die): New file.
* lib/openat.h (openat_save_die, openat_restore_die): Declare and define.
* m4/openat.m4 (gl_FUNC_OPENAT): Add openat-die.c.