revlog: clarify the non sparse-revlog case in `issnapshot` If we are not using sparse-revlog, there is only one type of snapshot, the full one.

exthelper: switch to using the registrar merging method

registrar: add a method to merge registrar instances This provides sanity checking beyond simply merging the underlying dictionaries.

phabricator: ensure that the return of urlopener.open() is closed No problem observed, just an oversight noticed while reading documentation.

revlog: fix pure python slicing test when chain contains nullrev The revlog mock used in the test was not behaving the same as its C counterpart.

merge with stable

remotefilelog: fix bug in maybesparsematch returning alwaysmatcher The description of the method says that it should return None if sparse is not used in this repository; since sparse.matcher() returns alwaysmatcher if sparse is not enabled, I'm using that as the signal to return None here to preserve the previous behavior. Differential Revision: https://phab.mercurial-scm.org/D5487

procutil: correct spelling of uninterruptable -> uninterruptible Differential Revision: https://phab.mercurial-scm.org/D5488

help: show advanced, experimental and deprecated extensions with --verbose I noticed that phabricator and absorb weren't showing up, no matter what. There's a related problem where commands for these extensions *do* show up without --verbose. I'm not sure what the point of hiding the extensions, but not the commands is.

help: remove a duplicate category name entry for TOPIC_CATEGORY_NONE