cache: group obscache and revsfiltercache invalidation in a single function Both caches are very volatile and needs invalidation on the same kind of event. revsfiltercache actually depends on the content of revsfiltercache.

clfilter: use filtering in `visibleheads` This is the second real use of changelog filtering. The change is very small to allow testing the new filter with a setup close to the original one. We replace custom post processing on `heads`function by call to the standard code pass on a filtering repo. In later coming will have wider usage of filtering that will make the dedicated function useless.

clfilter: use filtering in `visiblebranchmap` Here is the first real use of changelog filtering. The change is very small to allow testing the new filter with a setup close to the original one. We replace custom post processing on branchmap function by call to the standard code pass on a filtering repo. In later coming will have wider usage of filtering that will make the dedicated function useless.