May 2016 XFS reverse-mapping, reflink, and online fs scrub

[Darrick J. Wong]

I've pushed the rmap+reflink patches to github.  The kernel patches are against
4.6-rc6, the xfsprogs patches against for-next, and xfstests patches are
against master, same as last time.

I /think/ the overlapped interval btree is working correctly, and it's now
in djwong-devel.  The xfstests should all pass except generic/924 (check that
we can't swapon a reflink file) and xfs/128 (swapextents is broken with rmap).

djwong-experimental now contains the start of adding log intent items for
deferred operations.

--D

Semi-sane:
https://github.com/djwong/linux/commits/djwong-devel
https://github.com/djwong/xfsprogs/commits/djwong-devel
https://github.com/djwong/xfstests/commits/djwong-devel
https://github.com/djwong/xfs-documentation/commits/djwong-devel
https://github.com/djwong/man-pages/commits/djwong-devel

HBD:
https://github.com/djwong/linux/commits/djwong-experimental
https://github.com/djwong/xfsprogs/commits/djwong-experimental