would be good to string-cast/sanitize version data

Right now, if an addon uses a non-string for version, openerp can no longer do module updates for anything (since only strings have the lower() function). It would be good to stringcast to ensure that you're dealing with a string. This change would include (but may not be limited to) changing parse_version.py line 73 from "for part in _parse_version_parts((s or '0.1').lower()):" to "for part in str(_parse_version_parts((s or '0.1').lower())):". I have this as a feature instead of a bug because technically if the existing code doesn't work, it means that an addon author used version incorrectly, but it's good to not have a big part of OpenERP functionality (update all modules) become unavailable because of that.