stunnel port deinstall is interactive.

[Stephen Hurd]

This isn't exactly a bug, but is correct but unexpected behaviour...

Uninstalling the stunnel port without PACKAGE_BUILDING set will prompt
to remove the stunnel user and group.  I did a portupgrade and set BATCH
to allow me to go to work and come back with everything updated.  When
I came back, it was waiting for input.

Now, the stunnel port is not interactive for install... and the ports
manpage describes BATCH as:
BATCH         If defined, only operate on a port if it can be installed
              100% automatically.

So really, because it's only prompted when deinstalling, that behaviour
is correct.  However, because portupgrade deinstalls a port before
upgrading it, I can't do an update without the possibility of needing
user interaction.

I don't feel completely comfortable setting PACKAGE_BUILDING as I can't
find it documented anywhere.

Is there some simple thing that I'm missing?  Should I just set
PACKAGE_BUILDING and be done with it?  Should I submit a patch?