Let's do that again.

Changelog:

* imenu.el (imenu--subalist-p): Don't error on non-conses and
allow non-lambda lists as functions.

In my opinion a predicate should not throw an error.  Anyway more
important is the `non-lambda' lists part.

(imenu--in-alist): Don't recurse into non-subalists.

Looking at the commentary, the ability to embed functions in a menu has
clearly been added after this functions was written.

(imenu): Don't pass function itself as an argument.

,----[ (info "(elisp) Imenu") ]
|      Selecting a simple element has the effect of moving to position
|      INDEX-POSITION in the buffer.  Special elements look like this:
| 
|           (INDEX-NAME INDEX-POSITION FUNCTION ARGUMENTS...)
| 
|      Selecting a special element performs:
| 
|           (funcall FUNCTION
|                    INDEX-NAME INDEX-POSITION ARGUMENTS...)
`----

(cddr index-item) == (FUNCTION . ARGS), is wrong as argument list, we
need one more cdr.

* doc/lispref/modes.texi: Make it clear that sub-alist is the cdr.

-ap