xfs: update for 3.20-rc1

This update contains:
o RENAME_EXCHANGE support
o Rework of the superblock logging infrastructure
o Rework of the XFS_IOCTL_SETXATTR implementation
	- enables use inside user namespaces
	- fixes inconsistencies setting extent size hints
o fixes for missing buffer type annotations used in log recovery
o more consolidation of libxfs headers
o preparation patches for block based PNFS support
o miscellaneous bug fixes and cleanups
Merge branch 'xfs-misc-fixes-for-3.20-4' into for-next