Quiet ThreadSanitizer

This is a false-positive, but only because programs semantics meant that
accessing the queue.count without taking the lock was "ok".  However,
tsan doesn't know this.  By moving the queue.count=0 line to before the
associated mutex is created, tsan doesn't warn any more.

Note that neither worker->exit nor worker->queue.count need to be set to
0, as that's done by the bzero call.
s/bzero/memset/

memset is what all the cool kids are using the days, including the POSIX
spec.  bzero(3) mentions that it has been deprecated and in fact removed
from POSIX.1-2008.
Merge pull request #3 from dgryski/tsan-warning-fix

Fix initialization order to quiet TreadSanitizer.