delete-trailing-whitespace and binary files

[Kim F. Storm]

I have delete-trailing-whitespace in before-save-hook, but that
was a real disaster editing etc/spook.lines ... as soon as
I saved the file, all the trailing NUL-characters were deleted.

What can be done about this?

1) If file is binary (how to check that?), don't delete whitespace
   when run from a hook (how to check that?).

Is there a "file-binary-p" function which tests if
a file contains any non-printable characters?

2) Don't consider NUL to be whitespace.

3) ?

-- 
Kim F. Storm <address@hidden> http://www.cua.dk