PostgreSQL support (initial revision)

This adds support for PostgreSQL as a database for selfoss. Tested with
pg 9.0, but anything reasonably modern (8.x+) should work.  Testing
platform is debian stable on i386 with pg 9.0.7 and php 5.3.3-7.

Squashed commit of the following:

commit d65487baf61b60112772e4778f2f4f23082ad5a0
Author: Michael Jackson <michael.o.jackson@gmail.com>
Date:   Thu Mar 14 22:11:38 2013 -0400

    Fixing another boolean/integer mismatch with pg

commit f325dfdb1fc02a3bf0e43d27dba52f0077a1018e
Author: Michael Jackson <michael.o.jackson@gmail.com>
Date:   Thu Mar 14 22:05:46 2013 -0400

    Further fixes for pg support

commit 041050cc99188671889a599b86677980b1e45d1a
Author: Michael Jackson <michael.o.jackson@gmail.com>
Date:   Thu Mar 14 21:50:28 2013 -0400

    Initial revision of support for postgresql database.