Log Message:
Updated to 112.24.00, and converted to use mk/fetch/github.mk.

- Reduce code generated by `pa_test` in favor of more code in `pa_test_lib`.
  + Less generated code means less time spent compiling it.
  + Reducing code in `pa_test.ml` is good, because:
      a) Staging semantics make this code hard to understand.
      b) This code is written using the less familiar revised OCaml syntax.
      b) We get less code to migrate to syntax extensions.

- Re-used location code in `pa_here`; side benefit that we get full path names
  in (Loc...) instead of just the file's basename.