[XFS] 929045 567344 This mod re-organizes some of the in-core file extent

[XFS] 929045 567344 This mod re-organizes some of the in-core file extent
code to prepare for an upcoming mod which will introduce multi-level
in-core extent allocations. Although the in-core extent management is
using a new code path in this mod, the functionality remains the same.
Major changes include:	- Introduce 10 new subroutines which re-orgainze
the existing code but	do NOT change functionality:
xfs_iext_get_ext()	   xfs_iext_insert()	     xfs_iext_add()
 xfs_iext_remove()	   xfs_iext_remove_inline()
xfs_iext_remove_direct()	 xfs_iext_realloc_direct()
xfs_iext_direct_to_inline()	    xfs_iext_inline_to_direct()
xfs_iext_destroy() - Remove 2 subroutines (functionality moved to new
subroutines above):	    xfs_iext_realloc() -replaced by xfs_iext_add()
and xfs_iext_remove()	      xfs_bmap_insert_exlist() - replaced by
xfs_iext_insert()	  xfs_bmap_delete_exlist() - replaced by
xfs_iext_remove() - Replace all hard-coded (indexed) extent assignments
with a call to	 xfs_iext_get_ext() - Replace all extent record pointer
arithmetic (ep++, ep--, base + lastx,..)   with calls to
xfs_iext_get_ext() - Update comments to remove the idea of a single
"extent list" and   introduce "extent record" terminology instead

SGI-PV: 928864
SGI-Modid: xfs-linux-melb:xfs-kern:207390a

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