Jens had said to replace blktrace.c when I felt confident in it. I've
fixed a couple of nagging issues today, and so far all my testing has
gone very well. Successful runs are definitely valgrind clean, and my
networking tests (both with and without sendfile) have gone very well.
Doing some sample "standard" local disk runs - doing the default 4X512
test I've posted results on recently - are coming up clean without any
drops (as opposed to the 4.4% drop rate seen with version 1.0 of blktrace).

I'm posting this version, in case anyone has some time to review things.
Note: as opposed to the other ones I posted this one overwrites
blktrace.c - the diffs make no real sense, so it's best to review a
patched version of blktrace.c

If my testing continues to go well, and no comments come in from the
field, I'll slap this on top of blktrace.c Monday or Tuesday next week
(9 or 10 February 2009).