package postgresql-9.5 9.5.3-0ubuntu0.16.04 failed to install/upgrade: subprocess installed post-installation script returned error exit status 2

This happened on upgrading from 14.04 LTS to 16.04 LTS

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: postgresql-9.5 9.5.3-0ubuntu0.16.04
ProcVersionSignature: Ubuntu 3.13.0-92.139-generic 3.13.11-ckt39
Uname: Linux 3.13.0-92-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
Date: Fri Aug 5 15:18:07 2016
ErrorMessage: subprocess installed post-installation script returned error exit status 2
InstallationDate: Installed on 2012-04-02 (1585 days ago)
InstallationMedia: Xubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1.1
 apt 1.2.12~ubuntu16.04.1
SourcePackage: postgresql-9.5
Title: package postgresql-9.5 9.5.3-0ubuntu0.16.04 failed to install/upgrade: subprocess installed post-installation script returned error exit status 2
UpgradeStatus: Upgraded to xenial on 2016-08-05 (0 days ago)