Change the alignment in C structs (wa, pa, sa, and so on) from 1 to 2
bytes. This prevents the SIGBUS when PDP-11 Unix V7 catches the
misalignment. This fixes hilo_p.pdpv7 in simh-pdp11.
Change ALIGN to document that sections have 2-byte alignment. This
change should have no effect, because the sections only contain 2-byte
values.