fossil: update to 2.10

Change log:

  *  Added support for [./serverext.wiki|CGI-based Server Extensions].
  *  Added the [/help?cmd=repolist-skin|repolist-skin] setting used to
    add style to repository list pages.
  *  Enhance the hierarchical display of Forum threads to do less
    indentation and to provide links back to the previous message
    in the thread.  Provide sequential numbers for all messages in
    a forum thread.
  *  Add support for fenced code blocks and improved hyperlink
    processing to the [/md_rules|markdown formatter].
  *  Add support for hyperlinks to wiki pages in the
    [/md_rules|markdown formatter].
  *  Enhance the [/help?cmd=/stat|/stat] page so that it gives the
    option to show a breakdown of forum posts.
  *  The special check-in name "merge-in:BRANCH" means the source of
    the most recent merge-in from the parent branch of BRANCH.
  *  Add hyperlinks to branch-diffs on the /info page and from
    timelines of a branch.
  *  Add graphical context on the [/help?cmd=/vdiff|/vdiff] page.
  *  Uppercase query parameters, POST parameters, and cookie names are
    converted to all lowercase and entered into the parameter set,
    instead of being discarded.
  *  Change the default [./hashpolicy.wiki|hash policy] to SHA3.
  *  Timeout [./server/any/cgi.md|CGI requests] after 300 seconds, or
    some other value set by the
    [./cgi.wiki#timeout|"timeout:" property] in the CGI script.
  *  The check-in lock interval is reduced from 24 hours to 60 seconds,
    though the interval is now configurable using a setting.
    An additional check for conflicts is added after interactive
    check-in comment entry, to compensate for the reduced lock interval.
  *  Performance optimizations.
  *  Many documentation improvements.

(gutteridge)