Update CodeIgniter.php

require(APPPATH.'config/constants.php') should be in front of require(BASEPATH.'core/Common.php') because Common.php uses some constants defined in constants.php.
diff --git a/system/core/CodeIgniter.php b/system/core/CodeIgniter.php
index c121162..1981c26 100644
--- a/system/core/CodeIgniter.php
+++ b/system/core/CodeIgniter.php
@@ -45,14 +45,7 @@
  *
  */
 	define('CI_VERSION', '3.0-dev');
-
-/*
- * ------------------------------------------------------
- *  Load the global functions
- * ------------------------------------------------------
- */
-	require_once(BASEPATH.'core/Common.php');
-
+	
 /*
  * ------------------------------------------------------
  *  Load the framework constants
@@ -69,6 +62,13 @@
 
 /*
  * ------------------------------------------------------
+ *  Load the global functions
+ * ------------------------------------------------------
+ */
+	require_once(BASEPATH.'core/Common.php');
+
+/*
+ * ------------------------------------------------------
  *  Define a custom error handler so we can log PHP errors
  * ------------------------------------------------------
  */
@@ -385,4 +385,4 @@
 	$EXT->call_hook('post_system');
 
 /* End of file CodeIgniter.php */
-/* Location: ./system/core/CodeIgniter.php */
\ No newline at end of file
+/* Location: ./system/core/CodeIgniter.php */