Pull up following revision(s) (requested by martin in ticket #1856):
sys/arch/vax/boot/xxboot/start.S: revision 1.5
sys/sys/bootblock.h: revision 1.55
sys/sys/disklabel.h: revision 1.113
usr.sbin/installboot/arch/vax.c: revision 1.14-1.15
Rearrange primary bootstrap slightly to free up all space between the disk
label and the uVAX rom boot parameter block.
Calculate the disklabel size (for asm code) dynamically based on MAXPARTITIONS.
Adapt to new vax primary bootstrap layout.
Fix installboot for VAX, as discussed on port-vax. Problem pointed out
by Jonny Billquist, thanks to Marl Pizzolato for patiently explaining
the various ways of booting a vax to me.
Now VAX 780 can boot directly from VMB.EXE again.
Provide an empty __CTASSERT() for toolbuilds

(msaitoh)