branchcache: use an explicit class for the v2 version
This prepare the introduction of an experimental v3 format version.
In the process, we move the description of the format in that new class.
$ cat >> $HGRCPATH << EOF
> [extensions]
> absorb=
> EOF
Abort absorb if there is an unfinished operation.
$ hg init abortunresolved
$ cd abortunresolved
$ echo "foo1" > foo.whole
$ hg commit -Aqm "foo 1"
$ hg update null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo "foo2" > foo.whole
$ hg commit -Aqm "foo 2"
$ hg --config extensions.rebase= rebase -r 1 -d 0
rebasing 1:c3b6dc0e177a tip "foo 2"
merging foo.whole
warning: conflicts while merging foo.whole! (edit, then use 'hg resolve --mark')
unresolved conflicts (see 'hg resolve', then 'hg rebase --continue')
[240]
$ hg --config extensions.rebase= absorb
abort: rebase in progress
(use 'hg rebase --continue', 'hg rebase --abort', or 'hg rebase --stop')
[20]