defined values instead of hard-coded values. Don't repeat the register
access part of the code 4 times times or triple-space statements. This
fixes half of the style bugs in rev.1.172.
Hardware flow control of 16650As is still officially unsupported. I
was mistaken about it being broken. It is broken in 16650s but is
fixed in 16650As except for the maximum trigger level (which is no
longer used). Testing of the 16650's broken hardware flow control
watermarks by programming them on 16950s showed that their effects are
not too bad if the fifo size and trigger level are reasonably large
(16 is much better than 8).
cd3aaf0e7c