Minor fixes for 160-bit disassembly:
(1) Print the default segment %ss before adresses relative to %bp.
This is too cluttered for me, but so is printing some other default prefixes, and this is a reasonable reminder that %ss is quite likely to be different from %ds in 16-bit mode. db_disasm still handles prefixes poorly, by trying to discard redundant ones. This loses information, and sometimes the result is wrong or misleading. Clean up nearby initializations and dead code.
(2) Fix decoding of operand and address size prefixes in 16-bit mode.
They reverse the default in all modes.
Obtained from: (1) is partly from r1.4 (2003/11/08) in DFlyBSD (?)