Fix not filter case for field occurrence typing
Small adjustment to bitmap-message%
Simplify tooltip.rkt port to TR
Type-check the distributed parts of world too
Loosen `this` argument type on method accessors

This *should* be sound, since the class macro should
guarantee that internal method accessors always receive
the right object when they are called. Thus, there should
be no way for the self instance type to be wrong.

Removing this eliminates redundant type errors that
occur when the whole class itself doesn't type-check.