Updated disconnect for persistent connections

[JargonMan]

The db2_pconnect allows persistent connections to be made in the connect function, but the db2_close function in the disconnect function does not close those connections. This change allows a boolean to be passed to the disconnect function with a value of true that will allow a persistent connection to be closed.

[froschdesign]

This violates the interface. See:

zend-db/src/Adapter/Driver/ConnectionInterface.php

Lines 42 to 47 in 9acb8f9

	/**
	* Disconnect
	*
	* @return ConnectionInterface
	*/
	public function disconnect();

[JargonMan]

Good point.

Could we implement something like this from the connect function; it seems like overkill and I wasn't sure if the connectionParameters were reliable to make the determination on the db2_close vs db2_pclose.

if (is_resource($this->resource)) {
        return $this;
    }
    // localize
    $p = $this->connectionParameters;
    // given a list of key names, test for existence in $p
    $findParameterValue = function (array $names) use ($p) {
        foreach ($names as $name) {
            if (isset($p[$name])) {
                return $p[$name];
            }
        }
        return;
    };
$isPersistent = $findParameterValue(['persistent', 'PERSISTENT', 'Persistent']);