Another baby step toward getting sysinstall working:

Another baby step toward getting sysinstall working:

o fillin media s/h/c fields from new XML phk just added; need this because
  sysinstall uses them in the fdisk look-alike
o add new tags to xml parser
o cleanup parser a touch; remove unused tags and move tag parsing stuff to
  a table to simplify future additions
o redo callback to pass 64-bit values since mediasize overflows u_int32_t
o loosen parsing sanity checks a touch to deal with new xml we must handle
o move sector size probing to non-geom handling since we now get it from xml
o remove WHOLE_DISK_SLICE buggery now that we get mediasize from xml