exchange: move bundle specification parsing from cmdutil Clone bundles require a well-defined string to specify the type of bundle that is listed so clients can filter compatible file types. The `hg bundle` command and cmdutil.parsebundletype() already establish the beginnings of a bundle specification format. As part of formalizing this format specification so it can be used by clone bundles, we move the specification parsing bits verbatim to exchange.py, which is a more suitable place than cmdutil.py. A subsequent patch will refactor this code to make it more appropriate as a general API.

revset: add optional offset argument to limit() predicate It's common for GUI or web frontend to fetch chunk of revisions per batch size. Previously it was possible only if revisions were sorted by revision number. $ hg log -r 'limit({revspec} & :{last_known}, 101)' So this patch introduces a general way to retrieve chunk of revisions after skipping offset revisions. $ hg log -r 'limit({revspec}, 100, {last_count})' This is a dumb implementation. We can optimize it for baseset and spanset later.

revset: port limit() to support keyword arguments The next patch will introduce the third 'offset' argument. This allows us to specify 'offset' without 'n' argument.