http2 update integration

https://github.com/warmcat/libwebsockets/issues/489



This

1) fixes the vhost changes on master

2) works around the ah pool changes

3) fixes some other build problems that appeared

4) hacks out physical flow control for internal streams

5) updates the advertised protocol to h2 needed by, eg, chrome 51

That gets it able to serve small (<4K, ie, one packet) files over http2

Signed-off-by: Andy Green <andy@warmcat.com>