[XFS] 929045 567344 This mod introduces multi-level in-core file extent

functionality, building upon the new layout introduced in mod
xfs-linux:xfs-kern:207390a.  The new multi-level extent allocations are
only required for heavily fragmented files, so the old-style linear extent
list is used on files until the extents reach a pre-determined size of 4k.
4k buffers are used because this is the system page size on Linux i386 and
systems with larger page sizes don't seem to gain much, if anything, by
using their native page size as the extent buffer size. Also, using 4k
extent buffers everywhere provides a consistent interface for CXFS across
different platforms.  The 4k extent buffers are managed by an indirection
array (xfs_ext_irec_t) which is basically just a pointer array with a bit
of extra information to keep track of the number of extents in each buffer
as well as the extent offset of each buffer.  Major changes include:  -
Add multi-level in-core file extent functionality to the xfs_iext_  
subroutines introduced in mod:	xfs-linux:xfs-kern:207390a  - Introduce 13
new subroutines which add functionality for multi-level   in-core file
extents:	 xfs_iext_add_indirect_multi()	      
xfs_iext_remove_indirect()	   xfs_iext_realloc_indirect()	      
xfs_iext_indirect_to_direct()	      xfs_iext_bno_to_irec()	    
xfs_iext_idx_to_irec()	       xfs_iext_irec_init()	   
xfs_iext_irec_new()	    xfs_iext_irec_remove()	  
xfs_iext_irec_compact() 	xfs_iext_irec_compact_pages()	     
xfs_iext_irec_compact_full()	     xfs_iext_irec_update_extoffs()

SGI-PV: 928864
SGI-Modid: xfs-linux-melb:xfs-kern:207393a

Signed-off-by: Mandy Kirkconnell <alkirkco@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>