order of image searching in texinfo

[Graham Percival]

Hi all,

In the essay, we'd like to use high-quality pdf images for the pdf
backend, and (relatively) low-quality pngs for info and html
backends.

According to the texinfo manual,
  http://www.gnu.org/software/hello/manual/texinfo/Image-Syntax.html
the pdfTeX backend reads .png, .jpg, .jpeg, and .pdf, **in that
order**.  This is precisely backwards to what we want.  :(
There's the optional _extension_ argument, of course, but that
only works for makeinfo.  :(:(


Our current solution is to move such images into a new
  Documentation/pictures/pdf/
and use
  @iftex
  @image{pictures/pdf/OpusAndFeta,,,}
  @end iftex
  @ifnottex
  @sourceimage{OpusAndFeta,,,png}
  @end ifnottex

in the texinfo file.  I'm not wild about this solution, but it's
the best I can see.  Can anybody improve on this?

Cheers,
- Graham