[boost] fusion - reverse_view on maps

Hello, Awhile back I was using fusion.reverse_view on a fusion.map sequence (I think it was ~<=1.37 or thereabouts.) In later upgrades this became broken as a bidirectional concept was enforced on the reverse_view (quite sensible.) To work around this I made a minor change to my version which allowed reverse_view to work on both bidirectional sequences and those meeting the is_associative trait. Anyway, it got me wondering if there is a good reason that the map type doesn't model a bidirectional sequence? Cheers, Brandon