+ - state_file and avail_file periodicity is now easier to express
+ (check the documentation) the old behavior should still work.
+ * Storage: not backward compatible, but it seems that nobody ever used it
+ - Remove attribute 'content_type' of <storage_type>: was never used
+ - Make attribute 'model' of <storage_type> optional: for future usage
+ - Remove Bconnection model property: was never (in)validated. Replaced by
+ the maximum of the read and write bandwidth as a resource constraint.