PostgreSQL bundle issue on clean Debian 7

Resolves issue during bundle install `sudo -u git -H bundle install --deployment --without development test mysql aws`:

    Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
    
        /usr/local/bin/ruby extconf.rb
    checking for pg_config... no
    No pg_config... trying anyway. If building fails, please try again with
     --with-pg-config=/path/to/pg_config
    checking for libpq-fe.h... no
    Can't find the 'libpq-fe.h header
    *** extconf.rb failed ***
    Could not create Makefile due to some reason, probably lack of necessary
    libraries and/or headers.  Check the mkmf.log file for more details.  You may
    need configuration options.

    Provided configuration options:
            --with-opt-dir
            --without-opt-dir
            --with-opt-include
            --without-opt-include=${opt-dir}/include
            --with-opt-lib
            --without-opt-lib=${opt-dir}/lib
            --with-make-prog
            --without-make-prog
            --srcdir=.
            --curdir
            --ruby=/usr/local/bin/ruby
            --with-pg
            --without-pg
            --with-pg-dir
            --without-pg-dir
            --with-pg-include
            --without-pg-include=${pg-dir}/include
            --with-pg-lib
            --without-pg-lib=${pg-dir}/
            --with-pg-config
            --without-pg-config
            --with-pg_config
            --without-pg_config


    Gem files will remain installed in /home/git/gitlab/vendor/bundle/ruby/2.0.0/gems/pg-0.15.1 for inspection.
    Results logged to /home/git/gitlab/vendor/bundle/ruby/2.0.0/gems/pg-0.15.1/ext/gem_make.out
    An error occurred while installing pg (0.15.1), and Bundler cannot continue.
    Make sure that `gem install pg -v '0.15.1'` succeeds before bundling.