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

mkdir a
cd a
hg init
echo foo > b
hg add b
hg ci -m "b" -d "1000000 0"

chmod -w .hg

cd ..

hg clone a b

chmod +w a/.hg # let test clean up

cd b
hg verify