wireproto: allow unbundle with hashed heads parameter (issue2126) Current wire protocol of unbundle sends the list of all heads in the remote repository to avoid race condition. This causes "URL too long" error on HTTP server when the repository has many heads. This change allows clients to send SHA1 hash of sorted head hashes instead. Also, this introduces "unbundlehash" capability to inform them that the server accepts hashed heads parameter.

merge with stable

encoding: avoid localstr when a string can be encoded losslessly (issue2763) localstr's hash method exists to prevent bogus matching on lossy local encodings. For instance, we don't want 'caf?' to match 'café' in an ASCII locale. But when café can be losslessly encoded in the local charset, we can simply use a normal string and avoid the hashing trick. This avoids using localstr's hash method, which would prevent a match between