xfs: update for 4.2-rc1

This update contains:

o A new sparse on-disk inode record format to allow small extents to
  be used for inode allocation when free space is fragmented.
o DAX support. This includes minor changes to the DAX core code to
  fix problems with lock ordering and bufferhead mapping abuse.
o transaction commit interface cleanup
o removal of various unnecessary XFS specific type definitions
o cleanup and optimisation of freelist preparation before allocation
o various minor cleanups
o bug fixes for
	- transaction reservation leaks
	- incorrect inode logging in unwritten extent conversion
	- mmap lock vs freeze ordering
	- remote symlink mishandling
	- attribute fork removal issues.
Merge branch 'xfs-misc-fixes-for-4.2-3' into for-next