Fixes for push corner case
TAH found a bug where push would push things the remote already had,
raising an assertion. This turned out to be because the changeset
protocol was not recording a common subset node in one case.
Also discovered was that the protocol was queueing multiple copies of
a node for pull. Fixed by changing fetch to a hash.
Add some more debugging output.
1:3aa14bbc23d9
0:8633637036c1
3aa14bbc23d9 tip
8633637036c1
8633637036c1+
8633637036c1
3aa14bbc23d9 tip
merging file1
3aa14bbc23d9 tip
3aa14bbc23d9 tip
3aa14bbc23d9 tip
3aa14bbc23d9 tip