wireprotoframing: record when new stream is encountered
Without this, we choke after receiving the 2nd frame in a stream.
Not sure how we made it this far without finding this bug.
Differential Revision: https://phab.mercurial-scm.org/D3334
httppeer: handle error response from client reactor
With this in place, we're now seeing useful errors when running
tests with the new wire protocol enabled!
Differential Revision: https://phab.mercurial-scm.org/D3332