clfilter: drop unnecessary explicit filtering on rebase Hidden changeset filtering is now done at repo level. The rebaseset computation will not include any (unless you add --hidden).

clfilter: ensure that hidden filtering is working on all commands Now that hidden changeset are filtered for all commands, we test the behavior of `heads` and `summary` regarding hidden changeset.

clfilter: enforce hidden changeset globally The dispatch code now enables filtering of "hidden" changesets globally. The filter is installed before command and extension invocation. The `--hidden` switch is now global and disables this filtering for any command. Code in log dedicated to changeset exclusion is removed as this global filtering has the same effect.