bug#17685: 24.3.91.1; help-C-file-name failes to create temp buffer " *DOC*"

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> emacs -Q
> (find-lisp-object-file-name 'visible-bell 'defvar) ;visible-bell is just an
> example and can be replaced with any variable.

> RESULT:
> C-source

> EXPECTED RESULT:
> "src/dispnew.c"

Here's the reason for the behavior:
the DOC file is moderately large, so we don't want to load it into
memory just because the user did C-h v visible-bell RET.

So we only populate the *DOC* buffer when the user actually clicks on
the "C-source" link to jump to the source code.  And once the buffer is
populated, then there's no reason not to use it, so if *DOC* exists then
we do use it.

We could probably change it so that we always populate the *DOC* buffer
in the case where the C sources are available (so the behavior would
stay unchanged for users running pre-compiled Emacs, while it would
work better for those users who compile it themselves and keep the
source in place).  But I'm not sure it'd really be an improvement.


        Stefan