Migrations: fail on PHP 5.3.x

fixes #1006

library/Director/Db/Migrations.php

@@ -5,6 +5,7 @@ namespace Icinga\Module\Director\Db;
 use DirectoryIterator;
 use Exception;
 use Icinga\Application\Icinga;
+use Icinga\Exception\IcingaException;
 use Icinga\Module\Director\Data\Db\DbConnection;
 
 class Migrations
@@ -23,6 +24,13 @@ class Migrations
 
     public function __construct(DbConnection $connection)
     {
+        if (version_compare(PHP_VERSION, '5.4.0') < 0) {
+            throw new IcingaException(
+                "PHP version 5.4.x is required for Director >= 1.4.0, you're running %s."
+                . ' Please either upgrade PHP or downgrade Icinga Director',
+                PHP_VERSION
+            );
+        }
         $this->connection = $connection;
         $this->db = $connection->getDbAdapter();
     }