WIP

commit 43466aae47bfcd2ad9bf501faec8e75c08095e4f
Author: Max Grossman <max.grossman@delphix.com>
Date:   Mon Dec 9 10:37:51 2013 -0800

    4370 avoid transmitting holes during zfs send
    4371 DMU code clean up
    Reviewed by: Matthew Ahrens <mahrens@delphix.com>
    Reviewed by: George Wilson <george.wilson@delphix.com>
    Reviewed by: Christopher Siden <christopher.siden@delphix.com>
    Reviewed by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
    Approved by: Garrett D'Amore <garrett@damore.org>