Added NSF value-checker "cr_item_of_package" for quick checks for valid parameters
This checker is especially useful when processing external values (query-parameters etc). Since the check involves a DB lookup, it is no suited inside busy loops.
By the change, one can now specifiy the sorting type for the ordered composite. The sorting type can be "integer", "real", "index" or "dictionary" (default "dictionary"). If the sorting type is set to "index", the mixin ::xo::OrderedComposite::IndexCompare is added automatically.