convert/svn: make sink recover gracefully from empty changeset
Otherwise when processing a changeset that in fact changes no files
(perhaps due to bug in import from CVS) can get something like:
unexpected svn output:
abort: unable to cope with svn output
Bug report and patch draft by Jesse Glick <jesse.glick@sun.com>
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
pulling from ../B1
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
bar should remain deleted.
f9b0e817f6a48de3564c6b2957687c5e7297c5a0 644 foo
pulling from ../A2
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
bar should remain deleted.
f9b0e817f6a48de3564c6b2957687c5e7297c5a0 644 foo