xfs: update for 3.16-rc1

This update contains:
o cleanup removing unused function args
o rework of the filestreams allocator to use dentry cache parent lookups
o new on-disk free inode btree and optimised inode allocator
o various bug fixes
o rework of internal attribute API
o cleanup of superblock feature bit support to remove historic cruft
o more fixes and minor cleanups
o added a new directory/attribute geometry abstraction
o yet more fixes and minor cleanups.
Merge branch 'xfs-misc-fixes-3-for-3.16' into for-next