stablerange: add an sql index on subranges id too This should speed up query that find super ranges.

obshashrange: less brutal reset when receiving markers on existing node We now target the affected ranges only. The implementation is still slow but that should be better than what we had before.

obshashrange: update the cache updating logic Use the more modern option when available. (Same as the other caches).

stablerange: cleanup the update logic

stablesort: cleanup the update logic

firstmergecache: cleanup the update logic

depthcache: cleanup the update logic

changelog: add an entry about the obshashrange changes

stablerange: be more cautious when deleting the sql connection This triggered some crash in further development. This also match what is done elsewhere with this attribute.

stablerange: clarify sql transaction logic This should help concurrent access.

stablerange: use mergepoint based algorithm for the official stable range Changing the official stable range will impact all users of the infrastructure. We update version number of the cache file and discovery methods to clarify this. We do no keep compatibility with the old method over the wire. The new algorithm is much better and keeping compat is more work than we have time for right now.

stablerange: explicitly create a stablerange entry for branchpoint method We are about to change the default.

stablerange: have a mergepoint based sql backed class Everything is so generic that getting a class is 3 line of codes.

stablerange: introduce a sql backed version of the generic on disk cache This is getting use close to actually using the new sorting and algorithm for real.