Avoid calling cpu_nap() until after we have determined that there is
no input ready to read.  This avoids delaying for one timer interrupt
(~50ms) in the case of

  if ( iskey() )
     char = getkey()

which happens to be present in monojob.c, which is where we spend most
of our time looping (e.g. during any download).

This should eliminate the irritating tendency of gPXE to lose
keypresses.

Discovered on a Dell system where the serial port seems to send in a
constant stream of 0xff characters; this wouldn't be a problem in
itself except that each one triggers the 50ms delay (as mentioned
above), which really kills performance.

names.

Add "dev" pointer in struct net_device to tie network interfaces back to a
hardware device.

Force natural alignment of data types in __table() macros.  This seems to
prevent gcc from taking the unilateral decision to occasionally increase
their alignment (which screws up the table packing).