Another developer release - RT #52317 still not fixed when
reading from a pipe (as opposed to reading from a file, either
redirected to stdin or in @ARGV).
Fix RT #57391 (bug reported and suggested fix by Kevin Ryde):
duping STD(IN,OUT,ERR) may get it wrong when the "target"
filehandle is also some STD* filehandle, e.g.
run3 [ ... ], \undef, *STDERR, *STDOUT;
Fix RT #57394: display it prominently in the docs that
run3 uses system (and hence is subject to system's idiosyncrasies).