io_submit.stp: various fixes

[Jeff Moyer]

These fixes are pretty important for making the data gathered from
io_submit.stp useful.  Patches 1 and 3 I've been using for a while.
Patch 3 was developed recently due to issues collecting data on a
large cpu count system.

Cheers,
Jeff

[PATCH 1/3] io_submit.stp: fix array membership test
[PATCH 2/3] io_submit.stp: use an accumulator for traces
[PATCH 3/3] io_submit.stp: let the user know when the script is