purge: avoid full walks when directories aren't purged If match.traversedir is not None, we're forced to do full walks. However when we aren't purging directories we don't need to set match.traversedir to anything. This speeds up non-full walks such as the one hgwatchman makes possible. For mozilla-central with hgwatchman enabled, 'hg purge --files' goes from 0.88 seconds to 0.22.