port(1) manpage: better explain behavior of -N flag

[cooljeanius (Eric Gallager)]

Currently, man port has the following:

       -N
           Non-interactive mode, interactive questions are not asked

It would be nice if this could be clarified to better specify how exactly it behaves when the questions aren't asked. I'm assuming that it means that the behavior is as if the user just chose the default response to all questions? I'm wondering because I've been thinking that it might be nice to split the flag into 3:

• 1 that removes interactivity by assuming that the response is always "yes"
• 1 that removes interactivity by assuming that the response is always "no"
• 1 that removes interactivity by assuming that the response is whatever the default is (which is what I'm assuming the current behavior is)

Also, a conf option and/or environment variable to control this behavior would both be nice, too (primarily for CI systems).