Make expand_buffer() a non-inline function, so that we can add debug
messages.

Expandable buffers now don't *always* round up to the next power of two.
This allows e.g. loading a 137MB ISO image on a machine with only 256MB
RAM...

copy_{to,from}_phys.

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.

size.  (The restriction on the size of free blocks remains.)

easily from struct buffer.

refer to data outside of our data or stack segments.

addresses.  This will have to be reworked to use physical addresses thanks
to the PXE spec.