src != dest
instead of:
dest != src
I think that's less confusing and more consistent.
In do_postfix(), if ${SRC_DIR}/gnu/dist/postfix/conf doesn't exist and
${DEST_DIR}/usr/share/examples/postfix does, use the latter for the
${DEST_DIR}/etc/postfix checks. This means that postinstall can be
run in a temporary directory which has etc.tgz extracted into it
with -s `pwd`, (versus against a source tree), and the postfix upgrade
works correctly.
Remove some unnecessary goop.