Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 22265)
+++ wp-includes/functions.php	(working copy)
@@ -3794,3 +3794,14 @@
 function wp_checkdate( $month, $day, $year, $source_date ) {
 	return apply_filters( 'wp_checkdate', checkdate( $month, $day, $year ), $source_date );
 }
+
+/**
+ * Determine if a constant exists and evaluates to boolean true
+ *
+ * @since  3.5.0
+ *
+ * @return bool true|false
+ */
+function wp_constant( $constant ) {
+	return defined( $constant ) && constant( $constant );
+}