Description:
------------
I am not sure if this is a bug or a feature in terms of limits due to a test case exceeding internal limits.

Scenario #1.
Using session_regenerate_id() over 39 times results in the following errors:
Warning: session_regenerate_id() [function.session-regenerate-id]: Cannot regenerate session id - headers already sent

Scenario #2.
Using session_regenerate_id() over 19 times results in the following errors:
Warning: session_regenerate_id() [function.session-regenerate-id]: Cannot regenerate session id - headers already sent; when the following parameters are modified:
ini_set("session.entropy_file", "/dev/urandom");
ini_set("session.entropy_length", "512");
ini_set("session.hash_function", "sha512");


Test script:
---------------
session_start();

function _regenIDdef($old){
 session_regenerate_id(true);
 $_SESSION = $old;
}

function _prettyPrint($id, $i){
 echo sprintf('Iteration: %d : ID: %s => Length: %d<br/>', $i, $id, strlen((string)$id));
}

function _collide($array){
 $x=0;
 foreach($array as $k => $v){
  if (count(in_array($v, $array))>1){
   $x = $x++;
   echo sprintf('Collision found at %d session id %s<br/>', $k, $v);
  }
 }
 echo sprintf('Total collisions found %d<br/>', $x);
}

function _loop($id, $int){
 $a = array();
 for($i=0; $i<$int; $i++){
  _regenIDdef($id);
  _prettyPrint(session_id(), $i);
  $a[$i]=session_id();
 }
 _collide($a);
}

echo '<b>Testing with PHP defaults</b><br/>';
_loop(session_id(), 40, 'a');

echo '<b>Testing with /dev/urandom & entropy 32</b><br/>';
ini_set("session.entropy_file", "/dev/urandom");
ini_set("session.entropy_length", "512");
ini_set("session.hash_function", "sha512");
_loop(session_id(), 20, 'a');

?>

Expected result:
----------------
No errors returning about not being able to regenerate a new session_id

Actual result:
--------------
Warning: session_regenerate_id() [function.session-regenerate-id]: Cannot regenerate session id - headers already sent