hidden: invalidate hiddenrevs when needed The `hiddenrevs` cache is volatile too (It use content from `obscache`). When unsure it is invalidated when necessary. In a near future, the cache will probably be moved to `revsfiltercache`

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.

clfilter: introduce a "unserver" filtering mode This mode is for repository used as a server. It filter secret and hidden changeset out. It is put to use in later changeset.

clfilter: add a cache on repo for set of revision to filter for a given set. Recomputing the filtered revisions at every access to changelog is far too expensive. This changeset introduce a cache for this information. This cache is hold by the repository (unfiltered repository) and invalidated when necessary. This cache is not a protected attribute (leading _) because some logic that invalidate it is not held by the local repo itself.

clfilter: add actual repo filtering mechanism We add a `filtered` method on repo. This method return an instance of `repoview` that behaves exactly as the original repository but with a filtered changelog attribute. Filters are identified by a "name". Planned filter are `unserved`, `hidden` and `mutable`. Filtering the repository in place what out of question as it wont not allows multiple thread to share the same repo. It would makes control of the filtering scope harder too. See the `repoview` docstring for details. A mechanism to compute filtered revision is also installed. Some caches will be installed in later commit.

inotify: pacify pestiferous pyflakes precipitously

tests: make test-inotify-issue1208.t disappear

posix: move server side of unix domain sockets out of inotify We also turn the unix domain socket into a class, so that we have a sensible place to hang its logically related attributes and behaviour. We'll shortly want to reuse this in other code.