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.

#!/bin/sh
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "0 0"
ls
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "0 0"
hg co 0
# B should disappear
ls