Set _XOPEN_SOURCE to 600 to make fix FreeBSD build
Fix bug in CC.do.
Some cleanup
Refactor out handle_c and fix > 8096 reading bug
Rename diem to fatal to further confuse matters.

It's actually pretty easy now, fatal() is used as a short cut for
appending the strerror'd errno, while die() is just the generic version
of printing errors that behaves just like fprintf(stderr, msg) + exit().