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.

changeset:   0:acb14030fe0a
tag:         tip
user:        test
date:        Thu Jan  1 00:00:00 1970 +0000
summary:     test

b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 a
a
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions