determine iSCSI boot parameters.

of execl().

(which was extremely heavy on calls to malloc()).

Moved include/command.h to include/gpxe/command.h, since it's
gPXE-specific.

in our commands.

reconnection mechanism.  This avoids the problems of trying to reuse
the TCP connection structure before the old connection has cleanly exited.

TCP_CLOSED state (i.e. after the final FIN/ACK exchange), and has been
removed from the list of TCP connections.

Remove the now-totally-obsolete sockaddr_in field from tcp.h.

anywhere other than offset 0 within the EEPROM, so we have to put our
settings at 0x100 instead.

http://www.microsoft.com/whdc/winlogo/hwrequirements.mspx as required
for iSCSI boot.  Note that options 204-206 are listed in the document
but don't seem to be defined anywhere on the web.

overhauling, but this is not the time to do it.

technically be necessary, because the "enable A20" command requires
only that the keyboard controller is ready to accept input (i.e. that
its input buffer is empty), and shouldn't also require that the
keyboard is ready to send output (i.e. that its output buffer is also
empty).  See http://www.smsc.com/main/tools/io-bios/42i.pdf section
3.1 ("Command Invocation") for a justification.

gateA20_set() is called on every real-mode transition (in case some
idiot piece of external code such as Intel's PXE stack decided it
would be fun to re-disable A20), so draining the keyboard buffer means
that we end up losing keypresses on some systems.  In particular, this
makes typing at the command line almost impossible, and causes
Etherboot to ignore Ctrl-Alt-Del.

We should really implement a gateA20_test() function to verify that
gate A20 has been correctly enabled, and think about adding other
commonly-used methods such as Fast Gate A20.

completely forgot I'd written ages ago.

this can probably be optimised down quite a lot.