Revert 14616, 14617.  Go back to the original syntax for toplevel directives, only allowing capitalized identifiers in addition to lowercase ones.  Split #show into variants #show_val, #show_type, etc,  and implement a generic #show which combines all the results.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14697 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02