Add 'ssl_verify' option for mysqli driver

MYSQLI_OPT_SSL_VERIFY_SERVER_CERT is an undocumented option that may not always be available.
Reference: http://svn.php.net/viewvc/php/php-src/trunk/ext/mysqli/tests/mysqli_constants.phpt?view=markup&pathrev=302897
diff --git a/system/database/drivers/mysqli/mysqli_driver.php b/system/database/drivers/mysqli/mysqli_driver.php
index 8d398c8..dd3cc77 100644
--- a/system/database/drivers/mysqli/mysqli_driver.php
+++ b/system/database/drivers/mysqli/mysqli_driver.php
@@ -142,6 +142,11 @@
 
 			if ( ! empty($ssl))
 			{
+				if ( ! empty($this->encrypt['ssl_verify']) && defined('MYSQLI_OPT_SSL_VERIFY_SERVER_CERT'))
+				{
+					$mysqli->options(MYSQLI_OPT_SSL_VERIFY_SERVER_CERT, TRUE);
+				}
+
 				$client_flags |= MYSQLI_CLIENT_SSL;
 				$mysqli->ssl_set(
 					isset($ssl['key'])    ? $ssl['key']    : NULL,