Description:
------------
In later versions of libmysqlclient 4.1 and 5.0 the api 
call mysql_stmt_close also clears mysql->net.error* 
values. 
 
This affects that mysql_prepare doesn't return an error 
with current version of libmysql. 

Reproduce code:
---------------
<?php

$mysql = new mysqli("localhost", "user", "password", "test");

if (!($stmt = $mysql->prepare("this will never work"))) {
    printf("Error: %s\n", $mysql->error);
}

$mysql->close();
?>

Expected result:
----------------
Error: You have an error in your SQL syntax; check the 
manual that corresponds to your MySQL server version for 
the right syntax to use near 'this will never work' at 
line 1 

Actual result:
--------------
Error: