A user recently reported that Halibut's font-file handling doesn't

work on Windows, because input files are never opened in binary
mode. Introduce a small piece of compensatory mechanism, which opens
files initially in binary mode and then reopens them as text if
they're determined not to match any binary file type. I hope.

git-svn-id: svn://svn.tartarus.org/sgt/halibut@8889 cda61777-01e9-0310-a592-d414129be87e