run merge program in repo root. before, merge program was run in user current directory. Well defined location is better for scripts. no more need to pass HG_ROOT to merge program now.

#!/bin/sh

mkdir t
cd t
hg init
echo a > a
hg add a
hg commit -m "test" -d "0 0"
hg verify
hg parents
hg status
hg undo
hg verify
hg parents
hg status