Description:
------------
I think the extension should either ignore i5_lib or throw an exception when i5_naming is set to DB2_I5_NAMING_ON.  What it actually does is it uses the i5_lib on the 2nd call to the connection.  This is a very hard to find bug

When making a connection with db2_pconnect with the options i5_lib set to a library and i5_naming set to DB2_I5_NAMING_ON the executed SQL on the first call to the connection uses the default library of the previous connection.  In the documentation, it states i5_lib is not valid if the connection is using system naming mode.  

Test Script:
In the test script below you'll see 4 connections are made to production and then 6 connections and sql calls are made to Development.  On the 1st connection to development it still goes against a PRODUCTION library.

PHP Documentation:
i5_lib - A character value that indicates the default library that will be used for resolving unqualified file references. This is not valid if the connection is using system naming mode.




Test script:
---------------
<?php
// Simulate connections to production applications
$db = connectToProduction('USER1','MYPASS');
$db = connectToProduction('USER2','MYPASS');
$db = connectToProduction('USER3','MYPASS');
$db = connectToProduction('USER4','WEBUSER');

$i = 0;
while($i <= 5) {

    // Simulate connection to development application 6 times
    $db = connectToDevelopment();

    $sql = "SELECT ENV FROM LIBTEST";
    $stmt = db2_prepare($db, $sql);
    $result = db2_execute($stmt);
    $row = db2_fetch_assoc($stmt);

    echo $row['ENV']."<br>";

    $i++;
}

function connectToProduction($username, $password)
{
    $db = db2_pconnect('*LOCAL', $username, $password,
        [
            'i5_naming' => DB2_I5_NAMING_ON,
            'i5_libl' => 'PRODLIB',
            'i5_lib' => 'PRODLIB'
        ]
    );
    if (!$db){throw new Exception('Connection failed');}
    echo "Production DB connection successful<br>";
    return $db;
}

function connectToDevelopment()
{
    $db = db2_pconnect('*LOCAL', 'WEBTEST', 'WEBTEST',
        [
            'i5_naming' => DB2_I5_NAMING_ON,
            'i5_libl' => 'DEVLIB',
            'i5_lib' => 'DEVLIB'
        ]
    );
    if (!$db){throw new Exception('Connection failed');}
    echo "Development DB connection successful<br>";
    return $db;
}


Expected result:
----------------
Production DB connection successful<br>
Production DB connection successful<br>
Production DB connection successful<br>
Production DB connection successful<br>
Development DB connection successful<br>
development
Development DB connection successful<br>
development
Development DB connection successful<br>
development
Development DB connection successful<br>
development
Development DB connection successful<br>
development
Development DB connection successful<br>
development

Actual result:
--------------
Production DB connection successful<br>
Production DB connection successful<br>
Production DB connection successful<br>
Production DB connection successful<br>
Development DB connection successful<br>
production
Development DB connection successful<br>
development
Development DB connection successful<br>
development
Development DB connection successful<br>
development
Development DB connection successful<br>
development
Development DB connection successful<br>
development