LP#1493824: Install PG 9.4 on Debian Wheezy and Ubuntu Trusty

LP#1493824: Install PG 9.4 on Debian Wheezy and Ubuntu Trusty

Debian Wheezy only ships with PG 9.1 by default.  Ubuntu Trusty has Pg
9.3.  Pg 9.4 is the recommended version for use with Evergreen going
forward and will be the required minimum version of PostgreSQL for use
with Evergreen 3.0.  Since we envision continuing to support Wheezy
and Trusty through the lifetime of Evergreen 3.0, we therefore help
the user out by adding the apt.postgresql.org repository for them and
install PostgreSQL version 9.4 on these operating systems.

This commit does the following:

1. Sets up the installer to use the PostgreSQL community's apt sources
in a new Makefile.debian target, debian_postgresql_repo.  This target
is run on Debian Wheezy and Ubuntu trusty during prerequisite
installation.

2. Installs PG 9.4 client on Wheezy and Ubuntu.

3. Installs PG 9.4 server in the server prerequisite targets for
Wheezy and Ubuntu.

4. Uses pg_config in installation of lidbdi-drivers from source.

5. Updates the server installation document to reflect the above
changes.

6. Updates the server upgrade documentation to reflect the new minimum
(9.3) and recommended (9.4) PostgreSQL versions.

Benjamin Shum is the primary author of these changes, though they are
based on Chris Sharp's idea for using the PostgreSQL community apt
source.

The libdbi-drivers installation was fixed by Jason Stephenson who also
added an if block to skip the apt.postgresql.org repository set up if
it is already configured on the target host.

Signed-off-by: Ben Shum <ben@evergreener.net>
Signed-off-by: Jason Stephenson <jason@sigio.com>