* 'rhsummary' and 'rhmanifest' for reducing the number of hg command calls.
* 'rhdiff' for compatibility with Mercurial < 1.1.
Also renamed TEMPLATES_DIR to HELPERS_DIR because the directory now contains
templates and a helper extension.
Original version was written by Alessio Franceschelli,
downloaded from http://www.redmine.org/attachments/3395/overhaul.py
Contributed by Alessio Franceschelli and Yuya Nishihara.
