Major revamping (ver 2.0)

Major revamping (ver 2.0)

After a lot of fighting with maintaining a tree-styled design (each trace
having it's own node), it was just getting too cumbersome to work in all
circumstances. Taking a clue from blkparse itself, I decided to just keep
track of IOs at queue time, and updating fields based upon later traces.

The attached (large) patch works much faster, handles larger test cases
with less failures, and is managing some pretty large jobs I'm working on
(large Oracle-based DB analysis - 32-way box w/ lots of storage).

I've also added a Q2Q seek distance feature - it's come in handy when
comparing results of IO scheduler choice: We can see what the incoming IO
seek distances are (at queue time), and then see how the scheduler itself
manages things (via merges & sorting) by looking at D2D seek distances
generated.

As noted in the subject, I arbitrarily bumped this to version 2.00 as the
innards are so different. The documentation (btt/doc/btt.tex) has been
updated to reflect some minor output changes. I also fixed a bug dealing
with process name notification: there was a problem that if a new PID came
up with a name that was previously seen, btt wouldn't keep track of it
right. [When running with Oracle, a lot of processes have the same name but
different PIDs of course.]

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>