match: de-flake test-doctest.py by not depending on util.dirs() order util.dirs() yields directories in arbitrary order, which has made test-doctest.py flaky. I think they have been flaky since d8e55c0c642c (util: make util.dirs() and util.finddirs() include root directory (API), 2017-05-16). Before that commit, I think util.dirs() would return at most one entry, so there was only one iteration order. This patch fixes the problem by making _rootsdirsandparents() return a set (whose __str__() is defined to be in sorted order, I believe). The only caller wanted a set anyway. Differential Revision: https://phab.mercurial-scm.org/D6432

perf: add an option to profile the benchmark section Running a perf command with --profile gather data for the whole command execution, including setup and cleanup. This can significantly alter the data. To work around this we introduce a new option, it trigger the profiling of only one iteration of the benchmarked section.

perf: add a `pre-run` option sometimes, the initial run is necessary to warm some cache that are not relevant for the current measurement. We add a new `perf.pre-run` option to specify a number of run of the benchmark logic that will happens before measurement are taken.