Add possibility to set a custom wait time for bosh connections

Hi, I've added the possibility to set a custom Wait time for Bosh Connections. This is useful when users want to initialize a connection server side and pass it to a client where 10sc timeout is short.

Default value stay 10seconds.

Example : 
var clientXmpp = new XMPP.Client({
              jid: JID
              password: PASSWORD,
              boshURL: BOSHURL,
              wait: '60'
});

Thank's !