optimize revlog.lookup when passed hex(node)[:...]
Instead of converting each node from the filenode to a hex form,
convert the arg to a bin form.
For a revlog with 26711 entries, doing 100 lookup:
before: ~18s
after : ~13s
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