BUG #13959: Missing tmpfile exclude conf for socket

The following bug has been logged on the website:

Bug reference:      13959
Logged by:          Jakov Sosic
Email address:      jsosic@gmail.com
PostgreSQL version: 9.4.1
Operating system:   CentOS 7
Description:

Systemd on EL7 and probably some Debian based distributions has service
called systemd-tmpfiles-clean. That service deletes everything from /tmp
that's not excluded via special files.

PgSQL stores socket under /tmp by default, and systemd-tmpfiles-clean can
actually delete it. To avoid this, PGSQL packages should bring a file which
excludes it's socket from being deleted by tmpfiles-clean.

This is an example of file:

cat >> /usr/lib/tmpfiles.d/postgresql.conf <<EOF
# systemd tmpfiles exclude file for pgsql
# pgsql software unfortunately stores some important files
# in /tmp which should not be deleted

# Exclude pgsql socket and lock files
x /tmp/.s.PGSQL.*
EOF