Fix: when registering fails, do not fire the REGISTERED event
Hack for servers that do not announce IBR support over BOSH

Some servers do not announce their IBR support in
<stream:features>, even tough they actually support IBR over
BOSH.

This commit adds a method register_even_if_not_announced().
When enabled, we will not listen to what the server is
telling us and send a IBR request anyways.

This is a ugly hack that violates the XMPP protocol.