Move some help functions from help-fns.el to help.el, which is preloaded.

Move some help functions from help-fns.el to help.el, which is preloaded.

They are now needed by eg the function `documentation' in some circumstances.

* lisp/help-fns.el (help-split-fundoc, help-add-fundoc-usage)
(help-function-arglist, help-make-usage): Move from here...

* lisp/help.el (help-split-fundoc, help-add-fundoc-usage)
(help-function-arglist, help-make-usage): ... to here.

* lisp/emacs-lisp/bytecomp.el (byte-compile-lambda): Do not load help-fns.

Fixes: debbugs:17001