cleanups in revlog.lookup - add comments - do a clean separation of the different cases - don't use a list of each possible node when doing the lookup, just keep the previous entry

#!/bin/sh

unset HGUSER
EMAIL="My Name <myname@example.com>"
export EMAIL

hg init test
cd test
touch asdf
hg add asdf
hg commit -d '1000000 0' -m commit-1
hg tip