PostgreSQL database driver (#5861)

* [test/database/list] Fix test list 4 being used in two different tests

* [database/postgres] PostgreSQL database driver

* [database/postgres] Make transactions work based on continuation scope.

* [database/postgres] Implement nested transactions

* eslint --fix

* Add database changes from earlier this week to the PostgreSQL driver.

* Fix typo

* Fix postgres.incrObjectFieldBy returning undefined instead of null when given NaN

* [database/postgres] Fix sortedSetsCard returning an array of strings.

* Update socket.io postgres adapter

* Fix PostgreSQL erroring when multiple updates are made to the same sorted set entry in a single operation.

Add a test case to catch this error.

* Fix lint errors.

* Only prune sessions on one instance in a cluster to avoid deadlocks.

They're caught and handled by the database server, but they spam the logs.

* Fix arguments.slice.

src/controllers/admin/database.js

@@ -25,6 +25,14 @@ databaseController.get = function (req, res, next) {
 						next();
 					}
 				},
+				postgres: function (next) {
+					if (nconf.get('postgres')) {
+						var pdb = require('../../database/postgres');
+						pdb.info(pdb.pool, next);
+					} else {
+						next();
+					}
+				},
 			}, next);
 		},
 		function (results) {