largefiles: add a 'debuglfput' command to put largefile into the store We add a new debug command able to add arbitrary new files into the largefile store. This will be useful for debugging, testing and other unholy usecase.

debug: add a 'debugdownload' command This command resolve and fetch and URL through the Mercurial logic. Mercurial logic add various headers (including authentication) while resolving an URL so the commands helps with building the same request Mercurial would be doing. A new test file is created because we'll add more logic regarding Mercurial download logic and it will grow to a reasonable size.

revsetlang: raise ParseError to report invalid format character It's more common in revset and templater than raising Abort. I have a couple more patches to address exceptions caused by bad format string passed to revset() template function.