revert: Make it clearer when not to use revert

progress: check stderr.isatty() before each print This prevents writing progress information to a non-tty stderr if one is swapped in after startup, which happens in `hg serve`.

http digest auth: reset redirect counter on new requests (issue2255) This fixes a regression introduced in a1e575b48563 when Mercurial reuses the auth handler for several requests and the redirect counter never is reset.

revset: deal with empty sets in range endpoints (spotted by Julian Cowley <julian@lava.net>)