@id duplication in <descrules> handling with multiple <title>s.

[pobocks]

In handling of <descrules> with multiple child <titles>, the contents of <descrules> get replicated into a <descriptivenote> per each <conventiondeclaration> - if the titles or other content contained within <descrules> carries @id attributes, they will get duplicated. I think it would probably make sense to have the contents copied solely into the first <conventiondeclaration>, thus avoiding this possibility.