tests/test-dirstate-backup.t

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

Set up

  $ hg init repo
  $ cd repo

Try to import an empty patch

  $ hg import --no-commit - <<EOF
  > EOF
  applying patch from stdin
  abort: stdin: no diffs found
  [255]

No dirstate backups are left behind

  $ ls .hg/dirstate* | sort
  .hg/dirstate