tests/test-children.out

convert: fix mercurial_sink.putcommit

Changeset 4ebc8693ce72 added some code to putcommit to avoid creating a
revision that touches no files, but this can break regular conversions
from some repositories:

- conceptually, since we're converting a repo, we should try to make
  the new hg repo as similar as possible to the original repo - we
  should create a new changeset, even if the original revision didn't
  touch any files (maybe the commit message had some important bit);

- even if a "regular" revision that doesn't touch any file may seem
  weird (and maybe even broken), it's completely legitimate for a merge
  revision to not touch any file, and, if we just skip it, the
  converted repo will end up with wrong history and possibly an extra
  head.

  As an example, say the crew and main hg repos are sync'ed.  Somebody
  sends an important patch to the mailing list.  Matt quickly applies
  and pushes it.  But at the same time somebody also applies it to crew
  and pushes it.  Suppose the commit message ended up being a bit
  different (say, there was a typo and somebody didn't fix it) or that
  the date ended up being different (because of different patch-applying
  scripts): the changeset hashes will be different, but the manifests
  will be the same.

  Since both changesets were pushed to public repos, it's hard to recall
  them.  If both are merged, the manifest from the resulting merge
  revision will have the exact same contents as its parents - i.e. the
  merge revision really doesn't touch any file at all.

To keep the file filtering stuff "working", the generic code was changed
to skip empty revisions if we're filtering the repo, fixing a bug in the
process (we want parents[0] instead of tip).

% init
% no working directory
% setup
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
% hg children at revision 3 (tip)
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
% hg children at nullrev (should be 0 and 3)
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
% hg children at revision 1 (should be 2)
changeset:   2:8f5eea5023c2
user:        test
date:        Thu Jan 01 00:00:02 1970 +0000
summary:     2

1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% hg children at revision 2 (other head)
% hg children -r null
changeset:   0:4df8521a7374
user:        test
date:        Thu Jan 01 00:00:00 1970 +0000
summary:     0

changeset:   3:e2962852269d
tag:         tip
parent:      -1:000000000000
user:        test
date:        Thu Jan 01 00:00:03 1970 +0000
summary:     3

% hg children -r 0
changeset:   1:708c093edef0
user:        test
date:        Thu Jan 01 00:00:01 1970 +0000
summary:     1

% hg children -r 1
changeset:   2:8f5eea5023c2
user:        test
date:        Thu Jan 01 00:00:02 1970 +0000
summary:     2

% hg children -r 2
% hg children -r 3
% hg children -r 0 file0 (should be 2)
changeset:   2:8f5eea5023c2
user:        test
date:        Thu Jan 01 00:00:02 1970 +0000
summary:     2

% hg children -r 1 file0 (should be 2)
changeset:   2:8f5eea5023c2
user:        test
date:        Thu Jan 01 00:00:02 1970 +0000
summary:     2

1 files updated, 0 files merged, 1 files removed, 0 files unresolved
% hg children file0 at revision 0 (should be 2)
changeset:   2:8f5eea5023c2
user:        test
date:        Thu Jan 01 00:00:02 1970 +0000
summary:     2