While I've been upgrading my system, I've started pg_upgradecluster via dpkg-
menu that I've been shown while upgrading. `pg_upgradecluster` failed and I
never knew why (Thought I suspect that was due to lack of disk space).

I suspect we should improve dpkg update scripts, so they properly deal the
situation when `pg_upgradecluster` fails, report user tail of the
pg_upgradecluster output and informs where one can see full log (I really hope
there is a full log)

Since I both perl developer and deal with PostgreSQL core code on regular
basis I can provide patches for these functionality, if Debian PostgreSQL
Maintainers approve the idea.