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.

requesting all changes
abort: error: Connection refused
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ls: copy: No such file or directory
requesting all changes
abort: HTTP Error 404: File not found
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