BUG #12630: Postgres APT script issues

The following bug has been logged on the website:

Bug reference: 12630
Logged by: Tom
Email address: r(dot)andom(dot)dev4+postgres(at)gmail(dot)com
PostgreSQL version: 9.4.0
Operating system: Ubuntu 14.04.1 LTS
Description:

Using the postgres repo (http://apt.postgresql.org/pub/repos/apt/)

After 9.4 pg_upgrade, you are prompted to run ./delete_old_cluster.sh.

However, doing so breaks the postgres apt scripts. For example, running
'sudo apt-get remove postgresql-9.3 postgresql-9.3-ip4r
postgresql-client-9.3 postgresql-contrib-9.3' yields an erroneous error that
prevents uninstallation :

* Stopping PostgreSQL 9.3 database server
* Error: /var/lib/postgresql/9.3/main is not accessible or does not exist
...fail!
invoke-rc.d: initscript postgresql, action "stop" failed.
dpkg: error processing package postgresql-9.3 (--remove):
subprocess installed pre-removal script returned error exit status 1
Errors were encountered while processing:
postgresql-9.3
E: Sub-process /usr/bin/dpkg returned an error code (1)

Similarly the init script breaks too :
* Restarting PostgreSQL 9.3 database server
* Error: /var/lib/postgresql/9.3/main is not accessible or does not exist
...fail!