rhg: stop manifest traversal when no more files are needed Stopping the traversal early can skip a significant part of the manifest traversal, to avoid some of its cost. The worst-case benchmarks are favorable, as well. Running [hg cat] on the last file in the manifest of a large repo, I'm seeing a ~4ms improvement (150ms -> 146ms), so this time is now almost indistinguishable from the baseline ("brute force") implementation. Running [hg cat] on ~220 files together with the last file of the repo is further improved by ~5ms or so. I suspect the raw performance improvements are caused by splitting the manifest search and the file data access into separate phases, instead of interleaving them. Differential Revision: https://phab.mercurial-scm.org/D11616