feature request: more control over opening links

["Samuel Wales" <samologist@gmail.com>]

Summary: C-u C-u to force opening in an external application.

Detail:

My ideal settings for opening links would by default have
org-open-at-point and org-open-at-point-global open
everything in emacs except for anything that makes little
sense to open in emacs, such as PDF (whether http:// or a
local filename).  This would include html pages on the web,
which I want opened in emacs-w3m by default.

Then, for cases where that does not work, C-u would open in
emacs always.  C-u C-u would open in external always.
"External" here means the OS default (e.g. the "open"
command in OS X).

That way, when I know that I want something different, I can
force it.  (An alternate design is to reverse the sense of
what org-file-apps says.  But then you have to think about
what the default is and decide whether to reverse it.  This
seems an unnecessary cognitive burden.)

This seems not to be possible now.  If I set most things to
open in Emacs, I think that there is no way to open it in
the OS default.  Is that correct?