call MIME_RegisterConverters() to register the converter for documents
of type message/rfc822.
On Windows, that converter is currently only registered if SMART_MAIL is
defined.
On Mac, it's never registered at all.
Someone needs to consolidate all this.
This is a (mostly) unmodified version of lib/libnet
broken up into functional areas
It should be binary compatible with the lib created by lib/libnet
but is now 10 libs.
The only substantial things changed in the version is the include files