Clarified that warn() _always_ printed to STDERR, both in perl4
and perl5.
# perl4 prints: yup yup yup yup abc
# perl5 prints: abc
-=item * warn() specifically implies STDERR
+=item * warn() won't let you specify a filehandle.
+
+Although it _always_ printed to STDERR, warn() would let you specify a
+filehandle in perl4. With perl5 it does not.
warn STDERR "Foo!";