Tags: patch

The two patches below make Emacs use a dedicated type to represent
interpreted-function values.
    
Change `function` so that when evaluating #'(lambda ...)
we return an object of type `interpreted-function` rather than
a list starting with one of `lambda` or `closure`.
The new type reuses the existing PVEC_CLOSURE (nee PVEC_COMPILED)
tag used for byte-code function and tries to align the corresponding
elements:

- the arglist, the docstring, and the interactive-form go in the
  same slots as for byte-code functions.
- the body of the function goes in the slot used for the bytecode string.
- the lexical context goes in the slot used for the constants of
  bytecoded functions.

The first point above means that `help-function-arglist`,
`documentation`, and `interactive-form`s don't need to
distinguish interpreted and bytecode functions any more.

Main benefits of the change:

- We can now reliably distinguish a list from a function value.
  This removes some ambiguity in cases where the data can be made of
  a list or a function, such as `run-hooks` or completion tables.
- `cl-defmethod` can dispatch on `interactive-function`.
  Dispatch on `function` also works now for interpreted functions (but still
  won't work for functions represented as lists or as symbols, of course).
- Function values are now self-evaluating.  That was already the case
  when byte-compiled, but not when interpreted since
  (eval '(closure ...)) signals a void-function error.
  That also avoids false-positive warnings about "don't quote your lambdas"
  when doing things like `(mapcar ',func ...)`.


        Stefan