bug#8638: 24.0.50; Imenu should not include vacuous defvars

[Drew Adams]

> With lexical binding, (defvar foobar) is used to tell the bytecompiler
> that the variable has dynamic scope.

It's still a vacuous definition.  And any defvar tells the byte compiler that a
variable has dynamic scope, no?

This seems irrelevant to the bug report.  I'd still suggest removing vacuous
defvars from the menu.  Mixing in vacuous entries with entries that really
define variables distracts users.  You want to think that accessing a menu item
will take you to a real variable definition.

If someone wants to provide vacuous defvars in a different submenu from
`Variables' (e.g. `Vacuous Vars') I have no problem with that.  But I don't
really think that's needed.

FWIW, this is what I use in my code (imenu+.el):

(concat "^\\s-*("
        (regexp-opt
          '("defvar" "defconst" "defconstant" "defcustom"
            "defparameter" "define-symbol-macro") t)
        "\\s-+\\(\\sw\\(\\sw\\|\\s_\\)+\\)"
        "\\s-+[^) \t\n]")

Not perfect, perhaps, but it seems to do the job OK so far.