merge with crew-stable

dispatch: handle empty `testedwith` value in extension When extensions had an empty `testedwith` attribute the code tried to parse it and failed. As a result the actual error were shallowed by a This crash. We now treat empty strip as 'unknown'

destroyed: filter unknown before computing branchcache Branchcache of filtered version need up to date phase data.

branchmap: disable fallback to unfiltered branchcache Disables this simple optimisation to allow coming more powerfull approach: cache collaboration. Our goal is to have branchcache collaborate. This means that unfiltered branchcache will fallback to some filtered branchcache if invalid. We can't have the filtered branchcache to use the unfiltered one. That would loop.