Provide better context for custom Python encode/decode filters. While some can function with just some text and an optional command name, others may want a repository object, a ui object, and a file path. Use the enhanced information to good effect in win32text.dumbdecode's warning.

Register data filters in a localrepo instead of util - Changing data filters implementation is easier, adddatafilter() can rewrap filter after inspecting their prototype - Custom data filters really belongs to localrepo, mixing them with generic wrapper like "pipefilter" or "tempfilter" looks wrong. - util.filtertable should not be accessed from extensions

hgweb: forgot to centralize the req.write() calls in hgwebdir