HEADERS and flow control

Currently HEADERS are not subject to flow control. There are a couple of
reasons for this, but the biggest one is that this helps to prevent a
deadlock which can occur when a server is waiting for a particular request
before it can make progress on other responses, but flow control is
asserted.

One of the potential users of HTTP2 whom I've spoken with wished strongly
that HEADERS after the first complete HEADERS block on a stream would be
subject to flow control. AFAICT, this would work better than what we have
today, without potentially triggering the deadlock scenario for many
non-browser usecases.

Thoughts?

-=R