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
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown