tests/test-merge4.t

bundle2: introduce `replycaps` part for on-demand reply

The bundle2 processing does not create a bundle2 reply by default anymore.  It
is only done if the client requests it with a `replycaps` part. This part is
called `replycaps` as it will eventually contain data about which bundle2
capabilities are supported by the client.

We have to add a flag to the test command to control whether a reply is
generated or not.

  $ hg init
  $ echo This is file a1 > a
  $ hg add a
  $ hg commit -m "commit #0"
  $ echo This is file b1 > b
  $ hg add b
  $ hg commit -m "commit #1"
  $ hg update 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo This is file c1 > c
  $ hg add c
  $ hg commit -m "commit #2"
  created new head
  $ hg merge 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ rm b
  $ echo This is file c22 > c

Test hg behaves when committing with a missing file added by a merge

  $ hg commit -m "commit #3"
  abort: cannot commit merge with missing files
  [255]