Move db_select() call from CI_DB_driver::initialize() to db_connect()
so that it's only called by drivers that need it ('mysql', 'mssql').

As proposed in issue #2187.
diff --git a/system/database/drivers/mssql/mssql_driver.php b/system/database/drivers/mssql/mssql_driver.php
index f60071e..0836fa8 100644
--- a/system/database/drivers/mssql/mssql_driver.php
+++ b/system/database/drivers/mssql/mssql_driver.php
@@ -106,6 +106,18 @@
 			return FALSE;
 		}
 
+		// ----------------------------------------------------------------
+
+		// Select the DB... assuming a database name is specified in the config file
+		if ($this->database !== '' && ! $this->db_select())
+		{
+			log_message('error', 'Unable to select database: '.$this->database);
+
+			return ($this->db_debug === TRUE)
+				? $this->display_error('db_unable_to_select', $this->database)
+				: FALSE;
+		}
+
 		// Determine how identifiers are escaped
 		$query = $this->query('SELECT CASE WHEN (@@OPTIONS | 256) = @@OPTIONS THEN 1 ELSE 0 END AS qi');
 		$query = $query->row_array();