- added some comments
- the "updating modules list" log appears only when actually updating the list
- similar code to read the module descriptor file is combined
- default values for some descriptor entries are given only once
- in particular, the default version is always 0, instead of 0 when
reading a descriptor for migration and 1.0 when writing its value in
database.
bzr revid: vmt@openerp.com-20110511103455-lqezcrjf2996j7mc