scm: mercurial: improvement latest_changesets without supporting tags and named branches (#4455).
Based on latest-changesets-improvements-2.diff of #6159. http://www.redmine.org/attachments/4332/latest-changesets-improvements-2.diff
Contributed by Yuya Nishihara.
Authored by: tmaruyama 2011-02-18
Parent: [r4867]
Child: [r4869]
