This adds a new timestamp message to blktrace, giving the timeofday when
we starting tracing. This helps user space correlate block trace events
with eg an application strace.

This requires a (compatible) update to blkparse. The changed blkparse
is still able to process traces generated by older kernels, and older
versions of blkparse should silently ignore the new records (because
they have a pid of 0).

Signed-off-by: Olaf Kirch <okir@suse.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>