TAKE - encapsulate delalloc handling

[Ananth Ananthanarayanan <ananth@xxxxxxxxxxxxxxxxxx>]

With these changes only a couple of paths
(shrink_mmap & swap) in core-linux are
aware of delalloc pages.

Date:  Fri Jul  7 17:29:08 PDT 2000
Workarea:  dbear.engr.sgi.com:/build2/ananth/slinx24-xfs-new

The following file(s) were checked into:
  bonnie.engr.sgi.com:/isms/slinx/2.4.0-test1-xfs


Modid:  2.4.0-test1-xfs:slinx:66170a
linux/mm/filemap.c - 1.49
http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/linux/mm/filemap.c.diff?r1=text&tr1=1.49&r2=text&tr2=1.48&f=h
linux/kernel/ksyms.c - 1.54
http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/linux/kernel/ksyms.c.diff?r1=text&tr1=1.54&r2=text&tr2=1.53&f=h
linux/include/linux/mm.h - 1.35
http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/linux/include/linux/mm.h.diff?r1=text&tr1=1.35&r2=text&tr2=1.34&f=h
linux/include/linux/fs.h - 1.52
http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/linux/include/linux/fs.h.diff?r1=text&tr1=1.52&r2=text&tr2=1.51&f=h
linux/fs/buffer.c - 1.38
http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/linux/fs/buffer.c.diff?r1=text&tr1=1.38&r2=text&tr2=1.37&f=h
linux/fs/xfs/linux/xfs_iops.c - 1.56
http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/linux/fs/xfs/linux/xfs_iops.c.diff?r1=text&tr1=1.56&r2=text&tr2=1.55&f=h
linux/include/linux/page_buf.h - 1.52
http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/linux/include/linux/page_buf.h.diff?r1=text&tr1=1.52&r2=text&tr2=1.51&f=h
linux/fs/pagebuf/page_buf_io.c - 1.10
http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/linux/fs/pagebuf/page_buf_io.c.diff?r1=text&tr1=1.10&r2=text&tr2=1.9&f=h
        - Changes to isolate delalloc handling to a single address space 
operation.