BOSH support

[sander]

Add support for XEP-0124: Bidirectional-streams Over Synchronous HTTP (BOSH):
http://www.xmpp.org/extensions/xep-0124.html

The interface can stay the same. Just try to use BOSH over HTTP Binding if BOSH support is detected on the server.

[sander (s-devrieze)]

Servers that (will soon) have support for BOSH:
* Tigase: http://www.tigase.org/node/1362
* ejabberd: http://www.process-one.net/en/ejabberd/release_notes/release_note_ejabberd_200/
* Openfire: http://www.igniterealtime.org/builds/openfire/docs/latest/documentation/protocol-support.html

[Mats (matsben)]

I actually had a look at the XEP yesterday and it is fairly complex. Seems it also needs HTTP 1.1 which is also much more complex than 1.0. Instead I will try to make the old HTTP poll protocol work which it doesn't. Not sure what has happened. At least BOSH DNS TXT record support added in jlib::dns.