[Vortex] error in assumptions about MIME header format

[Sam Roberts]

Hi Francis,

I understand vortex doesn't have a full MIME parser in it, but I think
it should support at some of the common MIME variations. Currently, it
assumes "Content-Type: " introduces a content-type header, but MIME
specifies case-insensitive matching of header names (via ref to RFC822),
allows zero or no whitespace before and after the :, and also specifies
that media type/subtype comparisons are case-insensitive (sec 5.1,
rfc2045).

At the very least, an axl_icmp() function would be useful at
vortex_frame_factory.c:1021, and at vortex_greetings.c:235, but I didn't
see such a function in axl.

For now, I'm just hacking the other implementation to use same
conventions as vortex.

Cheers,
Sam