Restore dtrace hooks

This commit also rewrites a lot of the macros to play nicely with our
current command structure.

Change-Id: I9cd312a31c73ec605fff766ecc5a6188a87ded26
Reviewed-on: http://review.couchbase.org/39258
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>