hg: say 'hg update' instead of 'hg up' in merge status message
Includes the change to the message itself, along with several test
output files that also had to change.
adding a/b/c/d/x
adding a/b/c/d/y
adding a/b/c/d/z
moving a/b/c/d/x to z/b/c/d/x
moving a/b/c/d/y to z/b/c/d/y
moving a/b/c/d/z to z/b/c/d/z