* src/sort.c (cleanup): Clear temphead at the end.

* src/sort.c (cleanup): Clear temphead at the end.
(exit_cleanup): New function.
(main): Don't invoke atexit until we're ready.
Invoke it with exit_cleanup, not with cleanup and close_stdout,
to avoid a race condition with cleanup and signal handling.  More
details: http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/9508