No doc strings from DOC

[Juanma Barranquero]

After the last few changes to doc.c I get, for example:

M-x describe-function set-fill-function

Debugger entered--Lisp error: (wrong-type-argument stringp 0)
  ad-Orig-documentation(set-fill-column nil)
  documentation(set-fill-column)
  describe-function-1(set-fill-column)
  describe-function(set-fill-column)
  call-interactively(describe-function)
  execute-extended-command(nil)
* call-interactively(execute-extended-command)

but I believe that's just uncovering a previous bug (or build problem),
because previously, on my system (Windows XP, compiling with MSVC 6.0),
C-h f did not show documentation for functions in DOC. Perhaps it is
related to the problem in thread "Lost argument and doc string":

http://mail.gnu.org/pipermail/emacs-devel/2002-February/005583.html


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