make mdi and fetch/checksum

[Dieter Baron <dillo%danbala.tuwien.ac.at@localhost>]

hi,

currently, make mdi (the convenience target to compute distinfo)
downloads the new distfile from every available master site in turn
and then fails.

  That is because mk/checksum/checksum fails if no checksum is
recorded in the distinfo file (with exit code 2, as opposed to exit
code 1 on checksum mismatch), and that in turn causes mk/fetch/fetch
to retry with the next master site.

  mk/fetch/fetch should either succeed or abort on exit code 2, as
retrying is not going to help here.  If we want to abort, make mdi
needs a way to tell mk/fetch/fetch that no recorded checksum is not an
error (after all, we are trying to compute the checksum).

  Why do we currently consider no recorded checksum to be an error
while fetching?  Isn't that check better implemented in pkglint?

                                        yours,
                                        dillo