Fix up headers
The additions to owl.h and some of the removals were done by
Alejandro Sedeño <asedeno@mit.edu> in commit
77a0258b3919468fc9d7f7602588ac427ab36e6c.
Notes:
* I think owl.c lost the need for sys/time.h when we punted select() in
favor of glib's main loop.
* We don't actually need to include things like stdarg.h, stdio.h,
glib/gstdio.h, glib-object.h. I think they get indirectly included
via owl.h and/or glib.h. They're left in (or added in to) the files
that use functions/types from them.
* I'm not entirely sure what sys/socket.h is doing in message.c. It
is there from the initial commit. I suspect it might have had
something to do with the call to getnameinfo. message.c compiles
without it, but
http://pubs.opengroup.org/onlinepubs/009695399/functions/getnameinfo.html
suggests that we're supposed to include it? *shrugs* I'm leaving it
in, for now. (Rather, I'll leave one copy of the #include in.)
