emacsen-common: handling of add-on packages still broken in some cases

[Rob Browning <rlb@defaultvalue.org>]

[summary for debhelper/dh_installemacsen: there may be additional
 changes to policy soon.]

So I just realized that while I improved things a bit in 2.0.6/7, there
are still some broken cases.  In particular I believe that

  dpkg --purge emacsen-common

can cause trouble because emacsen-common will "rm -rf
/var/lib/emacsen-common".  That leaves all the add-on packages
installed, but missing their
/var/lib/emacsen-common/state/package/installed/ files.

Then if/when emacsen-common is reinstalled, say indirectly via

  apt-get install emacs24

none of the already installed add-on packages will be processed because
their state files are missing, and won't be recreated until the next
time they're upgraded or reinstalled.

All of these recent issues (and contemplating the fixes/workarounds)
make me suspect that it may have been unwise to try to make it possible
for add-on packages to have *no* emacs-infrastructure related
dependencies.

I'm not certain yet, but I believe that requiring add-on packages to
depend on emacsen-common (>> 2.0...) may make it much easier (and even
possible?) to handle the install/removal process correctly.

Currently, emacsen-common is only about 140k, and I don't expect it to
get much larger in the foreseeable future, so it doesn't seem like a
significant burden in exchange for what I think might be a much simpler,
and more obviously correct system.

As one example, the added dependency would allow us to remove the bit
just added to policy that required add-on packages to manually handle
their installed/state file.

I'm currently thinking it through, but please speak up if you have any
strong objections.  Otherwise we might add a "Depends: emacsen-common
..."  requirement (and simplify other relevant bits).

Apologies for the churn, and thanks.  I hope to get this sorted soon.
-- 
Rob Browning
rlb @defaultvalue.org and @debian.org
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