(make-autoload): Simplify docstring.

(make-autoload): Simplify docstring.
Make use of symbol-property doc-string-elt.
Use memq rather than a sequence of eq.
(doc-string-elt): Fix the wrong or missing previously unused values.
(autoload-print-form): New function extracted from
generate-file-autoloads to allow recursion when handling progn
so that defvar's and defun's docstrings are properly printed.
(generate-file-autoloads): Use it.