tests/test-issue842.t

wireprotov2: send content encoded frames from server

Now that we have support for negotiating encodings and configuring
an encoder, we can start sending content encoded frames from the
server.

This commit teaches the wireprotov2 server code to send content
encoded frames.

On the mozilla-unified repository with zstd enabled peers, this change
reduces the total amount of data transferred from server to client
drastically:

befor: 7,190,995,812 bytes
after: 1,605,508,691 bytes

Differential Revision: https://phab.mercurial-scm.org/D4927

https://bz.mercurial-scm.org/842

  $ hg init
  $ echo foo > a
  $ hg ci -Ama
  adding a

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo bar > a

Should issue new head warning:

  $ hg ci -Amb
  adding a
  created new head

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo stuffy > a

Should not issue new head warning:

  $ hg ci -q -Amc

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo crap > a
  $ hg branch testing
  marked working directory as branch testing
  (branches are permanent and global, did you want a bookmark?)

Should not issue warning:

  $ hg ci -q -Amd