separate xfer method.

Add missing .alloc_iob entries to several xfer_interface_operations
structures.

xfer_window() function, which can return a scalar rather than a
boolean.

present; DHCP is broken).

UDP API.

return a static buffer.

defined in vsprintf.h.  (This may change, since vsprintf.h is a
non-standard name, but for now it's the one to use.)

There should be no need to include vsprintf.h just for DBG() statements,
since include/compiler.h forces it in for a debug build anyway.

udp_connect() now follows the standard BSD sockets semantics and simply
sets the default address for outgoing packets; it doesn't filter incoming
packets.

Updated PXE API dispatcher to use copy_{to,from}_user, and moved to
arch/i386 since the implementation is quite architecture-dependent.
(The individual PXE API calls can be largely
architecture-independent.)

the Etherboot implementation (i.e. don't do what Intel did).

PXE code now compiles without errors (though it won't actually work).