raco decompile: show `provide`s
fix submodule export of enclosing module's binding

When `x` and `x`-with-a-mark are both defined, then the order of
definitions affected the binding that `(provide x)` would export
in a submodule that uses `#f` as its language. The problem was
in the implementation of the implicit `require`, which needs to
look up a variable's symbolic name in two different environments
to set up the right mapping.