store: switch to C-based hashed path encoding

pathencode: implement both basic and hashed encoding in C

pathencode: implement hashed encoding in C This will be used by an upcoming patch.

pathencode: implement the "mangling" part of hashed encoding in C This will be used by an upcoming patch.

pathencode: add a SHA-1 hash function This will be used by an upcoming patch. This calls out to the Python hash implementation. An earlier version of this function implemented SHA-1 directly, but the amount of extra code didn't seem like a good tradeoff compared to the small big-picture increase in performance (long paths are uncommon).

store: implement lowerencode in C

hgweb: run with "served" filter This changeset enable the "served" filter on all repo used by hgweb. Hgweb misbehave in a lot of when filtering changeset are present but I do not expect normal people to have secret or obsolete changeset on they server. Misbehavior will be gradually fixed later.

hgweb: walk the graph through the changelog This is necessary to enforce filtering. The result is a bit buggy (may provide less changeset than expected, but it will stop crashing on filtered revision access. Note that changelog.revs can not represents empty iteration like xrange did. So we have to explicitly prevent call when there is nothing to do.

hgweb: use changelog for iteration Iterating through changelog is necessary to enforce filtering.

hgweb: ignore filtered revision in revnav This changeset checks that a revision is known before adding it to the navigation. This will prevent traceback on filtered repository. This changeset result in an incorrect behaviors, Navigation link may be dropped without any replacement. However this bad navigation generation is much better than a crash