Backporting a fix to allow connection without dbname

The fix is already in master at
https://github.com/doctrine/dbal/commit/387eb5457498781e24716286a2511f5d030d63fb
but because it has not been backported the functionnality is still broken
for symfony 2.5 for instance.

Cherry pick to 2.4: [DBAL-717] Fix bug in MasterSlaveConnection with keepSlave option and switch back after transaction.

[DBAL-717] Fix bug in MasterSlaveConnection with keepSlave option and switch back after transaction.

Conflicts:
	tests/Doctrine/Tests/DBAL/Functional/MasterSlaveConnectionTest.php

[DDC-2310] [2.4] Fix evaluation of NOLOCK table hint on SQL Server

(cherry picked from commit 69931faa)

Add close() method in MasterSlaveConnection.php

Remove duplicate suggest section in composer.json

If you have a role "postgres" in PostgreSQL that is described like this:
```
-- Role: postgres
CREATE ROLE postgres LOGIN
  ENCRYPTED PASSWORD 'md53175bce1d3201d16594cebf9d7eb3f9d'
  SUPERUSER INHERIT CREATEDB CREATEROLE REPLICATION;
ALTER ROLE postgres IN DATABASE sf_test
  SET search_path = "$user", public, access, geographic, rrhh;
```

At the time when I execute the statement (Part of $schema value in the line 348):
```
SELECT string_to_array((select replace(replace(setting,"$user",user),' ','') from pg_catalog.pg_settings where name = 'search_path'),',')
```
I fetch this result:
```
{public," access"," geographic"," rrhh"}
```
Look the space character that is on the start of each string.This error does not match any namespace to which the role has access. This is critical when you have PostgreSQL database and you work with schemas.