new partition table scanning engine

[OKUJI Yoshinori]

  Because the original routine for scanning partition tables were
quite inflexible, I have rewritten a new engine. I have also fixed the
long-lived bug in the completion of BSD partitions, though it is still
not very clever. I'm going to make the command "find" more reliable
using the new engine.

  I have tested the engine with some partition tables, but it may have
bugs. Since it is essential for GRUB to recognize partitions
correctly, it is necessary to check if it works well in as many
environments as possible. So test it and send bug reports, if any. I'm
afraid that it may not work with a floppy formatted with a BSD
disklabel, although this wouldn't be very important, anyway.

Okuji