Check why `chk' fails.

Update 6809/const.h.

Produce bsd symbol tables.

Accept gas format.

Decide how to choose between 8-bit and 32-bit branches. 16-bit branches in
32-bit mode are unusable because top 16 bits of PC are messed up.

Limit insns to specified processor (warn for 386 insns on 8086).

Buffer for printing of listing.