stablerange: introduce a basic-mergepoint method
This method use the new 'mergepoint' based stable sorting. It is expected to be
eventually better than branch point to stable range: more stable, easier to
cache, etc. Having a basic implementation will allow use to validate more
advanced implementation.
#require test-repo pyflakes
Copied from Mercurial core (60ee2593a270)
$ cd "`dirname "$TESTDIR"`"
run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)
$ hg locate 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
> | xargs pyflakes 2>/dev/null