Description:
------------
Functions str_replace / str_ireplace give incorrect result when 'replace' argument is array filled with numbers.

Reproduce code:
---------------
<?php
$subject  = "*0-1-2-3-4-5-6-7-8-9*";
$search   = array ( "-", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" );
$replace  = array ( "+", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j" );
$result   = str_replace($search, $replace, $subject);
echo "$result\n"; // result is *a+b+c+d+e+f+g+h+i+j*
$replace  = array ( "+", "9", "8", "7", "6", "5", "4", "3", "2", "1", "0" );
$result   = str_replace($search, $replace, $subject);
echo "$result\n"; // result is *0+1+2+3+4+4+3+2+1+0* 
                  // must be   *0+1+2+3+4+5+6+7+8+9*
?>

Expected result:
----------------
the program output should be like this:
*a+b+c+d+e+f+g+h+i+j*
*0+1+2+3+4+5+6+7+8+9*

Actual result:
--------------
that`s what we get:
*a+b+c+d+e+f+g+h+i+j*
*0+1+2+3+4+4+3+2+1+0*