Clean up some merge logic - rename mode to branch_merge - use explicit update mode - use negative mtime for updates that set mtime - expand some cryptic variable names - elaborate merge dirstate comments - remove redundant manifest lookup for non-merge case - remove impossible merge case - fix up test cases

#!/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