(create_temp_file, xfopen, xfclose, write_bytes, sort_buffer_size,
fillbuf, main): Use it to regularize error messages. The only change
in behavior is that write_bytes and the final close used to say "write
error" but now give just the output file name, which should be enough.
Use fopen_safer, not fopen, to avoid subtle bugs when fopen returns
stdin, stdout, or stderr.
(xfclose): stdout is no longer a special case.
(main): Close output file, don't just flush it; there might be
an error on the close.
representing temp files. This improved CPU performance of
'sort -S 1 *.[ch]' by 17% on my host.
(struct tempnode): name member now uses struct hack.
(temphead): Now a pointer, not a structure. All uses changed.
(create_temp_file): Allocate node using struct hack.
(zaptemp): Free node using struct hack. Use pointer comparison, not
string comparison.
Defend against a DoS attack where someone else creates a
temporary file with the same name as ours. Use mkstemp to do
this, supplying our own mkstemp if the system doesn't have one.
Also, fix a race condition during cleanup on hosts without
sigaction.
(NAME_MAX_IN_DIR): Remove.
(sigprocmask, sigset_t): New macros, defined only on older hosts.
(caught_signals): New var.
(xtmpfopen, tempname): Removed.
(create_temp_file): New function, combining the functions of the old
xtmpfopen and tempname. All callers changed.
Use mkstemp to create the file.
(sighandler): On hosts without sigaction, ignore signals while
cleaning up, instead of letting them interrupt cleanup.
(main): Initialize caught_signals. On hosts with sigaction, block all
caught signals while handling one. Remove duplicate code.
