optionally turn encryption on or off in the XMPP connection

For identi.ca, we had some problems with the XMPP daemon getting
"stuck" in I/O through the encrypted (by default) XMPP socket. Turning
off encryption helped. So, now it's an option.

darcs-hash:20080826131814-84dde-2c4a809c6fb666dfb4b96d0d61205fe418f4e4b4.gz

config.php.sample

@@ -54,6 +54,7 @@ $config['db']['database'] = 'mysql://laconica:microblog@localhost/laconica';
 #$config['xmpp']['server'] = 'server.example.net';
 #$config['xmpp']['port'] = 5222;
 #$config['xmpp']['user'] = 'update';
+#$config['xmpp']['encryption'] = false;
 #$config['xmpp']['resource'] = 'uniquename';
 #$config['xmpp']['password'] = 'blahblahblah';
 #$config['xmpp']['public'][] = 'someindexer@example.net';