[boost] [Phoenix] Monomorphic functors don't expose result_type

I thought bind was supposed to generate monomorphic functors when used with function pointers, pointers to members, or monomorphic functors. Yet the functors it generates don't expose result_type, but only the result template. Moreover, I would expect functors to stay monomorphic when generating lambdas. If foo and bar are monomorphic (and thus expose result_type), foo < bar should be monomorphic too.