IMPORTANT: partition ID changed

[Matthias Drochner <drochner%zelux6.zel.kfa-juelich.de@localhost>]

I've just changed the ID for NetBSD in the MBR partition
table similarily to the i386.
The new ID is 169 dec, 0xa9 hex.
The kernel and the bootblocks will recognize the old ID
if COMPAT_386BSD_MBRPART is defined.

Unlike in the i386 port, coexistence of partitions with old
and new ID is not supported. (There is no other OS which
uses the old ID, and the implementation would be more
expensive due to the extended partition support.)

Unfortunately, I could not test the code at all, not even
check if it compiles.
Please report about problems.

best regards
Matthias