cleaning up courier-* packages

I started a large cleanup of courier packages (courier-authlib, and
courier-imap). I already get rid of triggers, duplicated config files,
and replaced original initialisation system with a standard one.

I'm curious however about the usefulness of conditional build options
and care about packages non included in the distribution, such as
vpopmail support in courier-authlib, and renaming of maildirmake in
courier-imap to avoid conflict with qmail. Are they really useful ?
Because otherwise, I'd rather drop them: simpler packages are easier to
maintain.