If no output file was specified sort fopened("/dev/stdout", "w").
This is *wrong* because "/dev/stdout" will truncate the output file,
thus undoing the append effect the shell had set up. The simple fix
here is to just arrange for outfp = stdout and don't play with /dev/stdout.
While I am here:
- KNF
- make pattern for mkstemp have 6 X's.
faf9e3e459