[bug-inetutils] ftp -p(assive) compatibility

[Karl Berry]

All the other ftp programs I've seen support -p to mean switch into
passive mode by default.  This is very useful, since so many places
(such as fencepost :() are configured to only work with passive mode.

Printing a command line prompt when not on a tty seems very obscure by
comparison.  How about leaving that as --prompt only, and changing -p
(aka --passive, I suppose) to do the passive mode thing?

Thanks,
Karl