Description:
------------
When switching on 0 (zero), control flow executes the wrong case.

Reproduce code:
---------------
<?php

$x = 0;
switch ($x) {
  case 'foo':
    print "foo == $x ?\n";
    break;
  case 0:
    print "0 == $x ?\n";
    break;
  default:
    print "default: \$x == $x  ?\n";
    break; }

?>


Expected result:
----------------
0 == 0 ?


Actual result:
--------------
foo == 0 ?