Issue #1355798 by Kjartan, xjm: Fixed Installer on PHP <5.3 results in parse...

Issue #1355798 by Kjartan, xjm: Fixed Installer on PHP <5.3 results in parse error instead of warning about old php.

core/install.php

@@ -15,8 +15,12 @@
 
 /**
  * Global flag to indicate that site is in installation mode.
+ *
+ * This constant is defined using define() instead of const so that PHP
+ * versions older than 5.3 can display the proper PHP requirements instead of
+ * causing a fatal error.
  */
-const MAINTENANCE_MODE = 'install';
+define('MAINTENANCE_MODE', 'install');
 
 // Exit early if running an incompatible PHP version to avoid fatal errors.
 // The minimum version is specified explicitly, as DRUPAL_MINIMUM_PHP is not