bug#11036: 24.0.94; imagemagick-render-type is void as a variable

[Glenn Morris <rgm@gnu.org>]

Obviously not for 24.1, but the following seems to work.
Anything that is in DOC should be defined at startup if relevant to the
platform in use.

I compared the results of `C-h f TAB' and `C-h v TAB' with and without
this change, and it just removes a few more void things.
Eg for me, the variables: motif-version-string, gtk-version-string, 
ns-initialized.


*** src/doc.c	2012-02-06 16:53:51 +0000
--- src/doc.c	2012-03-20 20:50:48 +0000
***************
*** 671,676 ****
--- 671,677 ----
  		  /* Install file-position as variable-documentation property
  		     and make it negative for a user-variable
  		     (doc starts with a `*').  */
+                   if (!NILP (Fboundp (sym)))
                      Fput (sym, Qvariable_documentation,
                            make_number ((pos + end + 1 - buf)
                                         * (end[1] == '*' ? -1 : 1)));
***************
*** 678,685 ****
  
  	      /* Attach a docstring to a function?  */
  	      else if (p[1] == 'F')
  		store_function_docstring (sym, pos + end + 1 - buf);
! 
  	      else if (p[1] == 'S')
  		; /* Just a source file name boundary marker.  Ignore it.  */
  
--- 679,688 ----
  
  	      /* Attach a docstring to a function?  */
  	      else if (p[1] == 'F')
+                 {
+                   if (!NILP (Ffboundp (sym)))
                      store_function_docstring (sym, pos + end + 1 - buf);
!                 }
  	      else if (p[1] == 'S')
  		; /* Just a source file name boundary marker.  Ignore it.  */