hgweb: handle a "descend" query parameter in filelog command When this "descend" query parameter is present along with "linerange" parameter, we get revisions following line range in descending order. The parameter has no effect without "linerange".

revset: add a 'descend' argument to followlines to return descendants This is useful to follow changes in a block of lines forward in the history (for instance, when one wants to find out how a function evolved from a point in history). We added a 'descend' parameter to followlines(), which defaults to False. If True, followlines() returns descendants of startrev. Because context.blockdescendants() does not follow renames, these are not followed by the revset either, so history will end when a rename occurs (as can be seen in tests).

context: add a blockdescendants function This is symmetrical with blockancestors() and yields descendants of a filectx with changes in the given line range. The noticeable difference is that the algorithm does not follow renames (probably because filelog.descendants() does not), so we are missing branches with renames.

url: support auth.cookiesfile for adding cookies to HTTP requests Mercurial can't currently send cookies as part of HTTP requests. Some authentication systems use cookies. So, it seems like adding support for sending cookies seems like a useful feature. This patch implements support for reading cookies from a file and automatically sending them as part of the request. We rely on the "cookiejar" Python module to do the heavy lifting of parsing cookies files. We currently only support the Mozilla (really Netscape-era) cookie format. There is another format supported by cookielib and we may want to consider using that, especially since the Netscape cookie parser can't parse ports. It wasn't immediately obvious to me what the format of the other parser is, so I didn't know how to test it. I /think/ it might be literal "Cookie" header values, but I'm not sure. If it is more robust than the Netscape format, we may want to just support it.