Description:
------------
Passing an array of integer values to stats_standard_deviation casts all of the 
values into floats. I didn't expect a simple calculation function to mutate the 
data in the input array.

Test script:
---------------
<?php
$data = array(2,3,2,2,2);
var_dump($data);
stats_standard_deviation($data);
var_dump($data);
?>

Expected result:
----------------
I would expect the two var_dump function calls to have identical output 
(identical as in identical value and type [ === ] not [ == ]).

array
  0 => int 2
  1 => int 3
  2 => int 2
  3 => int 2
  4 => int 2
array
  0 => int 2
  1 => int 3
  2 => int 2
  3 => int 2
  4 => int 2

Actual result:
--------------
array
  0 => int 2
  1 => int 3
  2 => int 2
  3 => int 2
  4 => int 2
array
  0 => float 2
  1 => float 3
  2 => float 2
  3 => float 2
  4 => float 2