Memory refinements now carry a boolean parameter that has the following
meaning:

[false] : Behave like a simple renaming of memories that merely allows to
          permute object identifiers. It does not allow to refine memories
          into a more defined version.
[true]  : Behave like before. Objects can be injected, and memory contents can
          be refined into a more defined variant.

We make refinements parametric in these two variant to avoid code duplication,
and because the [false] variant is a special case of the [true] variant.

For completeness of the executable semantics, we now use the [false] variant.