stablerange: introduce ondisk caching through sqlite There is many short cut and limitation with this first version of a cache but this allow use to envision some actual usage of the stablerange thingy so let us got for it.

stablerange: drop the cache on 'destroyed' if the repository have been strip, the cache is not usable as is. We could be smarter in the invalidation but that is a prototype anyway. G: changed hgext3rd/evolve/stablerange.py