clonebundle: support bundle2
exchange.readbundle() can return 2 different types. We weren't handling
the bundle2 case. Handle it.
At some point we'll likely want a generic API for applying a bundle from
a file handle. For now, create another one-off until we figure out what
the unified bundle API should look like (addressing this is a can of
worms I don't want to open right now).
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1