Ahh... http://tools.ietf.org/html/rfc5987

Yup, using 8859-1 for all header stuff seems good.  We should probably const it somewhere.  As it stand the iso-8859-1 references in the code will look like an arbitrary choice unless we use something  like HTTP_HEADER_ENCODING everywhere, and a link to the RFC in a comment where we define the const.