tests/test-convert-bzr-treeroot.t

revlog: fix pure version of _partialmatch() to include nullid

Before this patch, test-issue842.t and a few more tests fail when they
try to refer to the null revision by using a "000.." prefix of it (or
because they use the "shortest" template function which internally
does that).

This should have been part of my a3dacabd476b (index: don't allow
index[len(index)] to mean nullid, 2018-07-20), but I had forgotten to
update another part of the pure code there, so it didn't fail until
a1f934573c0b (parsers: adjust pure-python version to mimic
a3dacabd476b, 2018-08-09) and 65d5de1169dd (revlog: fix pure nodemap
to not access missing index entry, 2018-08-17) fixed the other things
I had missed.

Differential Revision: https://phab.mercurial-scm.org/D4332

#require bzr

  $ . "$TESTDIR/bzr-definitions"
  $ cat > treeset.py <<EOF
  > import sys
  > from bzrlib import workingtree
  > wt = workingtree.WorkingTree.open('.')
  > 
  > message, rootid = sys.argv[1:]
  > wt.set_root_id('tree_root-%s' % rootid)
  > wt.commit(message)
  > EOF

change the id of the tree root

  $ mkdir test-change-treeroot-id
  $ cd test-change-treeroot-id
  $ bzr init -q source
  $ cd source
  $ echo content > file
  $ bzr add -q file
  $ bzr commit -q -m 'Initial add'
  $ $PYTHON ../../treeset.py 'Changed root' new
  $ cd ..
  $ hg convert source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...
  1 Initial add
  0 Changed root
  $ manifest source-hg tip
  % manifest of tip
  644   file

  $ cd ..