[Pkg-postgresql-public] Bug#764705: postgresql-9.4: ERROR: The database format changed between beta 2 and 3. Please dump, but how?

[Thorsten Glaser]

Package: postgresql-9.4
Version: 9.4~beta3-1

Preparing to unpack .../postgresql-9.4_9.4~beta3-1_x32.deb ...
Stopping PostgreSQL 9.4 database server: main.
ERROR: The database format changed between beta 2 and 3. Please dump your 9.4 clusters first and remove them before upgrading the package.
dpkg: error processing archive /var/cache/apt/archives/postgresql-9.4_9.4~beta3-1_x32.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1

Uh, and…

… why doesn’t the preinst and postinst script do that for me?

… how do I do that, retaining all my databases, users, settings?

Would have been nice to have more help there, for people who
are *not* experienced PostgreSQL admins. I normally just use
pg_upgradecluster, and that works, which made the Debian pak‐
kages look good. But now?