bug#15296: 24.3.50; A macro object does not necessarily have `lambda' as its cadr

[Drew Adams <drew.adams@oracle.com>]

AFAICT, (elisp) `Defining Macros' is the closest thing we have to doc
telling you how to test whether a Lisp object is a macro.  There is no
`macro-p' predicate or similar in Emacs Lisp, unless I'm missing
something.  (Shouldn't there be?)

Anyway, this Elisp manual node says that a macro is a list whose car is
`macro' and whose `cdr' is a lambda expression.  That's not true if the
`defmacro' was byte-compiled.  The macro is then a list whose car is `macro'
but whose cdr is byte code, AFAICT.  So this will not work, for example:

(defun macro-p (obj)
  (and (fboundp obj)
       (let ((def  (symbol-function obj)))
         (and (consp def)
              (eq (car def) 'macro)
              (eq (cadr def) 'lambda)))))

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-08-23 on ODIEONE
Bzr revision: 113986 rgm@gnu.org-20130823185841-zoy6h1qk433ibrlf
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3' LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'