CONSTANT_Dynamic bootstrap signature restriction

[Daniel Heidinga]

>
>In discussions about future directions for CONSTANT_Dynamic, we've
>decided it would be helpful to restrict the set of legal bootstrap
>signatures. The first parameter type would be required to be declared
>with type MethodHandles.Lookup.

Dan, can you expand on why this restriction is helpful? It helps when 
evaluating a specification to have the rationale for the changes - both
for the EG and the observers.

Thanks,
--Dan