Description:
------------
it looks loke array_key_exists() makes a copy of the given array if there is a reference to that array. if there is no reference, everything works well.

Reproduce code:
---------------
// just to get the time in microseconds
function getmicrotime() {
   list($usec, $sec) = explode(" ",microtime());
   return ((float)$usec + (float)$sec);
}


$cnt = 2000;
$a = array_fill(0, $cnt, 'foo');


// this works as aspected very fast

$mtime = getmicrotime();

for ($i = 0; $cnt > $i; $i++)
	array_key_exists($i, $a);

echo getmicrotime() - $mtime . '<br>';


$b =& $a;  // making a reference, but not using it


// this will take a huge amount of time, but it's the same code as above

$mtime = getmicrotime();

for ($i = 0; $cnt > $i; $i++)
	array_key_exists($i, $a);

echo getmicrotime() - $mtime . '<br>';



Expected result:
----------------
the two loops should work the same.