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.
$ echo 'raise Exception("bit bucket overflow")' > badext.py
$ abspath=`pwd`/badext.py
$ echo '[extensions]' >> $HGRCPATH
$ echo "gpg =" >> $HGRCPATH
$ echo "hgext.gpg =" >> $HGRCPATH
$ echo "badext = $abspath" >> $HGRCPATH
$ echo "badext2 =" >> $HGRCPATH
$ hg -q help help
*** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
*** failed to import extension badext2: No module named badext2
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