obshashrange: use the dualsourcecache as a base for the cache
This will easily open the way to incrementally updated obshashrange cache.
Small update are needed to the data base schema so be bump the version
Currently the update function is not warming the cache (but details case where
it is invalidated).
#require test-repo
$ checkflake8() {
> if ! (which flake8 > /dev/null); then
> echo skipped: missing tool: flake8;
> exit 80;
> fi;
> };
$ checkflake8
Copied from Mercurial core (60ee2593a270)
$ cd "`dirname "$TESTDIR"`"
run flake8 if it exists; if it doesn't, then just skip
$ hg files -0 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
> | xargs -0 flake8