postgres driver requires pg or pg.js, as specified in config

Author: acobb

lib/driver/pg.js

@@ -1,5 +1,4 @@
 var util = require('util');
-var pg = require('pg');
 var semver = require('semver');
 var Base = require('./base');
 var type = require('../data_type');
@@ -220,6 +219,7 @@ var PgDriver = Base.extend({
 });
 
 exports.connect = function(config, callback) {
+    var pg = require(config.driver); //pg or pg.js, as defined in config
     if (config.native) { pg = pg.native; }
     var db = config.db || new pg.Client(config);
     callback(null, new PgDriver(db));