[cups] Can't detect file type / Not a PDF file

[Helge Blischke]

I’d file a bug at openprinting.org for the gstoraster (and possibly other) filter(s)
and suggest as a possible solution to read the environment variable
CONTENT_TYPE
instead
and check the contents for 
application/postscript
of
application/pdf

It is not necessary to strip the HP control statements, as Ghostscript’s PS interpreter
defines these as no ops.

Helge