Fix ticket:60.

This fixes the immediate issue, but there are still problems with
very long strings.  The bit-index for such strings won't fit in an
(unsigned-byte 32).

vm-fndb.lisp:
o Correct the defknown to have the correct arg types (vm::offset
  instead of index).

vm-tran.lisp:
o Update deftransform to use vm::offset instead of index.