racket: ,enter submodules

It is now possible to ,enter racket submodules.  This is only the
first part of the story, because evalations should take place in the
submodule, not in its top level module, as it happens now.
racket: ,gcd -> ,pwd

And we display it (the current path, settable via ,cd) as a string.
This was, i'm sure, a secret command nobody is using!
racket: indentation for module*
racket: handling correctly submodules in load handler during ,enter

That is, complying to the submodule loading protocol (cf. racket's own
enter!).
racket: module* and module+ denote submodules too

Recognizing those forms in the elisp module getter.
racket: C-u C-c C-z on a submodule enters it