[PATCH 0 of 2] issue2043: make merge --preview show all contributing changesets

[Greg Ward]

Fix for issue2043, "merge --preview hides some contributing changesets".

First patch is a minor tweak to a test script that made it easier for
me to understand what I was doing when I implemented the fix.  It
could easily be folded into the actual patch.

Second patch is the fix: it should speak for itself.

       Greg