bundlerepo: introduce method to find file starts and use it This moves us to the modern iter() technique instead of the `while True` pattern since it's easy. Factored out as a function because I'm about to need this in a second place.

bundlerevlog: use for loop over iterator instead of while True The iter() builtin has a neat pattern where you give it a callable of no arguments and a sentinel value, and you can then loop over the function calls like a normal iterator. This cleans up the code a little.

bundlerepo: use for loop over iterator instead of while True The iter() builtin has a neat pattern where you give it a callable of no arguments and a sentinel value, and you can then loop over the function calls like a normal iterator. This cleans up the code a little.

localrepo: jettison now-unused dirlog() method from localrepo