bug#12105: 24.1; `help-make-xrefs' should not create an xref to the current thingy

[Drew Adams]

Please exclude the current thingy that is being described from
cross-reference creation.  E.g., if I do `C-h f foo' and the doc for
`foo' happens to mention `foo' itself (using the `...' syntax), that
mention should not be turned into a cross reference (which just goes to
the same *Help* output).
 
This might mean adding an argument to `help-make-xrefs' to provide that
thingy.  And that might also mean adding the same arg to
`help-mode-finish'.  An alternative, I suppose, is to use a global
variable for the thingy being documented.

In GNU Emacs 24.1.1 (i386-mingw-nt5.1.2600)
 of 2012-06-10 on MARVIN
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include'