zeroconf: initial implementation This is a basic, hopefully portable, zeroconf extension. Enabling it will allow hg paths/pull/push/clone/etc. to automatically discover services advertised as "_hg". And naturally, running hg serve will advertise itself as a "_hg" service as well as a "_http" service for use by browsers.

churn and stats commands merged

Eliminate normpath from foldmap calls. Normcase already takes care of upper/lower case and /->\ conversions. What's left for normpath is folding of a/../a sequences but this should be either done consistently on both non-folding and folding code path or not at all, otherwise we are introducing inconsistent behavior between the two that has nothing to do with case folding. Second argument against it - normpath being pure Python function is very slow - as much as 50% of time is spend just inside normpath call on my repository.