Description:
------------
I have version 5.1.2. THIS MIGHT HAVE BEEN FIXED IN 5.2.1!!!

First use mysql_connect() on an included file and return the resource identifier and store this in a variable.
Then call session_start()
Now you have lost your resource identifier!
Calling session_start() first fixes the problem.

Reproduce code:
---------------
file1.php
function connect_to_db() {
  $link = mysql_connect($host, $user, $pass) or die(err_msg);
  mysql_select_db($db) or die(err_msg);
  return $link;
}
file2.php
include 'file1.php';
$link = connect_to_db();
echo $link;
session_start();
echo $link;

Expected result:
----------------
link resource id# ?
link resource id# ?

replace ? with a number

Actual result:
--------------
link resource id# ?
0