(main): Don't die when dev/ino of input and output are

(main): Don't die when dev/ino of input and output are
the same and the file descriptors correspond to stdin and stdout.
This is necessary on at least Digital UNIX (aka OSF1) 3.2C.
Otherwise, running `cat << X > $$' would fail with `cat: -: input
file is output file'.  From Jarkko Hietaniemi <jhi@epsilon.hut.fi>.