sanitize-commit: check for common spelling errors

Detect and complain about various English spelling errors/typos.
The spelling error dataset comes from the Lingua::EN::CommonMistakes
CPAN module; the feature is silently disabled if that module is not
installed.

Change-Id: Ie67984e43803683477549926cb39c61b96549966
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>