xfs: update for 3.9-rc1

For 3.9-rc1 there are primarily bugfixes and a few cleanups.

- fix(es) for compound buffers
- remove unused XFS_TRANS_DEBUG routines
- fix for dquot soft timer asserts due to overflow of d_blk_softlimit
- don't zero allocation args structure members after they are memset(0)
- fix for regression in dir v2 code introduced in commit 20f7e9f3
- remove obsolete simple_strto<foo>
- fix return value when filesystem probe finds no XFS magic, a
  regression introduced in 9802182.
- remove boolean_t typedef completely
- fix stack switch in __xfs_bmapi_allocate by moving the check for stack
  switch up into xfs_bmapi_write.
- fix build error due to incomplete boolean_t removal
- fix oops in _xfs_buf_find by validating that the requested block is
  within the filesystem bounds.
- limit speculative preallocation near ENOSPC.
- fix an unmount hang in xfs_wait_buftarg by freeing the
  xfs_buf_log_item in xfs_buf_item_unlock.
- fix a possible use after free with AIO.
- fix xfs_swap_extents after removal of xfs_flushinval_pages, a
  regression introduced in fb59581404a.
- replace hardcoded 128 with log header size
- add memory barrier before wake_up_bit in xfs_ifunlock
- limit speculative preallocation on sparse files
- fix xa_lock recursion bug introduced in 90810b9e82a3
- fix write verifier for symlinks