tests/test-revlog-group-emptyiter.t

bundle2: make server.bundle2.stream default to True

Support for bundle2 streaming clones has been shipped in Mercurial 4.5
(7eedbd5d4880), but was never activated by default. It's time to have more
people use it. The new format allows streaming clones to transport cache
(hooray for speed) and phaseroots (fixes phase-related issues).

Changes in tests:

bundle2 capabilities now have "stream=v2" (plus a '\n' as a separator) and
therefore take 14 bytes more: "%0Astream%3Dv2". Tip for tests that have data
encoded with CBOR: 0xd3 - 0xc5 = 14.

$USUAL_BUNDLE2_CAPS$ replaces $USUAL_BUNDLE2_CAPS_SERVER$, which is the same
thing, but without "stream=v2".

Since streaming clones now also transfer caches, the reported byte and file
counts are higher (e.g. 816 bytes in 9 files instead of 613 bytes in 4 files,
a bit of --debug and manual math confirms that the caches take these extra 203
bytes in 5 files).

Differential Revision: https://phab.mercurial-scm.org/D4680

Issue1678: IndexError when pushing

setting up base repo
  $ hg init a
  $ cd a
  $ touch a
  $ hg ci -Am a
  adding a
  $ cd ..

cloning base repo
  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd b

setting up cset to push
  $ hg up null
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ touch a
different msg so we get a clog new entry
  $ hg ci -Am b
  adding a
  created new head

pushing
  $ hg push -f ../a
  pushing to ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)

  $ cd ..