image:write-pnm doesn't work with SBCL 0.8.17

[Milan Zamazal]

Image writing in Backends/CLX/image.lisp breaks with SBCL 0.8.17.  The
output streams there are character streams, so if the environment is a
UTF-8 environment for instance, then the output stream is recoded and
the resulting image is broken.

Regards,

Milan Zamazal

-- 
When you're in a fight with an idiot, it's difficult for other people to tell
which one the idiot is.                       -- Bruce Perens in debian-devel