* '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.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4833 e93f8b46-1217-0410-a6f0-8f06a7374b81