perf: adds a cache to know if obsmarkers might affect a revision
Phase information still needs to be thrown in the mix to compute the final
information, but skipping reading the obsstore for most operation is a large
win.
Usage of this cache arrives in the next changeset.
#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