Print nicer error message when too old PHP version found - required by mysql driver (#1489099)

program/lib/Roundcube/rcube_db_mysql.php

@@ -34,6 +34,13 @@ class rcube_db_mysql extends rcube_db
      */
     protected function init()
     {
+        if (version_compare(PHP_VERSION, '5.3.0', '<')) {
+            rcube::raise_error(array('code' => 600, 'type' => 'db',
+                'line' => __LINE__, 'file' => __FILE__,
+                'message' => "MySQL driver requires PHP >= 5.3, current version is " . PHP_VERSION),
+                true, true);
+        }
+
         // SQL identifiers quoting
         $this->options['identifier_start'] = '`';
         $this->options['identifier_end'] = '`';