[pdftex] A rose, by any other name ... (.pdf extension)

[Piet van Oostrum]

It seems that with graphics inclusion by pdftex, the filename .pdf is
essential rather than the contents of the file.

The problem happens with xfig's relatively new export to `combined
PDF/LaTeX'. This format uses a LaTeX file (called xxx.pdftex_t) which
includes a PDF file with the \includegraphics command. However the PDF
file has extension .pdftex. Declaring:
\DeclareGraphicsRule{.pdftex}{pdf}{}{} makes pdftex recognize the
extension but it doesn't know how to get the image size:

! LaTeX Error: Cannot determine size of graphic in subnet.pdftex (no size speci
fed).

Renaming the file to .pdf and editing the .pdftex_t file solves it.
Apparently the rose smells differently if called by a different name.
Is there a way to let PDF find out the image size by recognizing the file
format rather than the name?
-- 
Piet van Oostrum <piet at cs.uu.nl>
URL: http://www.cs.uu.nl/~piet [PGP]
Private email: P.van.Oostrum at hccnet.nl