* fix twstat handling of mode bits * rejects incoming connections with a ridiculously small msize * allow "jumbo" (i.e. more than 16K) Twrite and Treads * allow Tread to read exactly msize bytes * kamiftp: fix reads wrt msize * kamiftp: do maximum reads and writes

don't use a constant: msize may be lower than that. Instead, use `msize - 4' which is guaranteed to be the maximum transferreable size. (it's not possible for msize to be lower than 4 since we reject ridiculously small msizes, so that difference can't underflow.)