[CM] Expose object_type_name/type-name

[bil at ccrma.Stanford.EDU]

I added type-name to s7.  I mostly use type-of with case,
so a symbol is handy.  To get the function, your can use
symbol->value.  Signatures use the symbols, so automatic
argument type checker macros can apply that value to the
argument.  The second argument to symbol->value is the let
to start the lookup in.  Or symbol-initial-value to get
its start-up binding.  I didn't want to introduce a bunch
of new symbols as type indicators (like '<integer>).