tests/test-empty-dir.t

rebase: fix --collapse when a file was added then removed

When a series of commits first adds a file and then removes it,
hg rebase --collapse prompts whether to keep the file or delete it. This is
due to it reusing the branch merge code. In a noninteractive terminal it
defaults to keeping the file, which results in a collapsed commit that is
has a file that should be deleted. This bug resulted in developers accidentally
commiting unintentional changes to our repo twice today, so it's fairly
important to get fixed.

This change allows rebase --collapse to tell the merge code to accept the
latest version every time without prompting.

Adds a test as well.

  $ hg init

  $ echo 123 > a
  $ hg add a
  $ hg commit -m "first" a

  $ mkdir sub
  $ echo 321 > sub/b
  $ hg add sub/b
  $ hg commit -m "second" sub/b

  $ cat sub/b
  321

  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cat sub/b 2>/dev/null || echo "sub/b not present"
  sub/b not present

  $ test -d sub || echo "sub not present"
  sub not present