Allow the passing of connection parameters to imap_open()

Since version 5.3.2 of PHP, imap_open() has an optional 6th
parameter which allows you to set certain connection parameters.

Currently the only key is:

- DISABLE_AUTHENTICATOR - Disable authentication properties

see https://bugs.php.net/bug.php?id=33500

Example of use:

  $server = new Server('imap.example.com', 993);
  $server->setParam('DISABLE_AUTHENTICATOR', 'GSSAPI');

This gets rid of the following errors:
<br />
<b>Notice</b>:  Unknown: Unknown GSSAPI failure: An invalid name was
supplied (errflg=1) in <b>Unknown</b> on line <b>0</b><br />
<br />
<b>Notice</b>:  Unknown: GSSAPI mechanism status: Hostname cannot be
canonicalized (errflg=1) in <b>Unknown</b> on line <b>0</b><br />