wireproto: client reactor support for receiving frames
We can now feed received frames into the client reactor and it will
validate their sanity, dispatch them appropriately.
The hacky HTTP peer has been updated to use the new code. No
existing tests changed, somewhat proving the code works as
expected.
Rudimentary unit tests for the new functionality have been
implemented.
Differential Revision: https://phab.mercurial-scm.org/D3224
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors