one should use VariationRangeCategory* instead of VariationCategory*:
if the resource does not use all items in a category, only Range methods
return the correct result.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@33611 20353a03-c40f-0410-a6d1-a30d3c3de9de