Fix traceback when nothing was added during unbundle
The changegroup and commit hook are now run only when
something is modified.
The correct number of changesets added is printed.
pulling from ../a
searching for changes
warning: pulling from an unrelated repository!
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg update' to get a working copy)
changeset: 1:9a79c33a9db3
tag: tip
user: a
date: Thu Jan 1 00:00:00 1970 +0000
summary: a
changeset: 0:01f8062b2de5
user: b
date: Thu Jan 1 00:00:00 1970 +0000
summary: b