tests/test-revlog-group-emptyiter.t

tests: demonstrate a problem with renames on the p2 side of a conversion

I think this is related to the octopus merge being sloppy, and that's having a
cascading affect on the fixup merge.  If this change is made on p1 (specifically
with the 'Added parent file' commit), the failure doesn't occur.

The file modification with the rename doesn't seem to be necessary, but it's
what's happening in a production repo where I first noticed, so I left it.  This
is an example of the manifest divergence I'd been seeing, which wasn't fixed by
Yuya's recent changes.  This is separate from the changelog divergence I was
also seeing[1].  Probably nobody cares about bzr anymore, but this will also
affect git, since the octopus fixup code is in the hg sink.

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-August/120473.html

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 ..