Fix SQL Server drivers and functional test suites

This should finally fix the functional test suites for SQL Server's `sqlsrv` and `pdo_sqlsrv` drivers. It introduces the following changes:

- Support for custom classes and constructor arguments with \PDO::FETCH_CLASS fetch mode when using `SQLSrvStatement::setFetchMode()`
- Fix fetch modes for `SQLSrvStatement::fetchAll()`
- Fix `SQLSrvStatement::fetchColumn()` for empty result sets
- Skip `BlobTest` for `pdo_sqlsrv` driver due to a bug in the driver when binding values to varbinary/blob type columns. See [DBAL-122](http://www.doctrine-project.org/jira/browse/DBAL-122) and [MSDN Post](http://social.msdn.microsoft.com/Forums/sqlserver/en-US/5a755bdd-41e9-45cb-9166-c9da4475bb94/how-to-set-null-for-varbinarymax-using-bindvalue-using-pdosqlsrv?forum=sqldriverforphp)
- Mention `pdo_sqlsrv` driver varbinary/blob limitations in documentation
- Add `sqlsrv` driver configuration documentation
- Fix schema manager functional test for retrieving column comments
- Fix SQL Azure functional tests (referenced non-existent classes)
- Fix `PDOConnection::bindParam()` signature's `$driverOptions` default value as `pdo_sqlsrv` driver errors with the wrong signature. See [here](http://php.net/manual/de/pdostatement.bindparam.php)

Please also note that the functional test suite will still fail if the underlying SQL Server database does not support SQL Azure as there currently is no reasonable way to distinguish those tests from SQL Server. Otherwise the tests now all pass!