Add testcase for bug #20993

tests/lang/bug20993.phpt

@@ -0,0 +1,23 @@
+--TEST--
+Bug #20993 (referenced array key, makes array global)
+--FILE--
+<?php
+$a = array(1);
+$b = array(1);
+$ref =& $a[0];
+
+echo $a[0], ' -b ', $b[0], ' -r ', $ref,  "\n";
+changeVal($a);
+echo $a[0], ' -b ', $b[0], ' -r ', $ref,  "\n";
+changeVal($b);
+echo $a[0], ' -b ', $b[0], ' -r ', $ref,  "\n";
+
+function changeVal($arr)
+{
+	$arr[0] = 2;
+}
+?>
+--EXPECT--
+1 -b 1 -r 1
+1 -b 1 -r 1
+1 -b 1 -r 1