TAKE - avoid recovery on root fs during boot

[Steve Lord <lord@xxxxxxx>]

if we remount the fs readonly, there is no need to put
out dummy log records to clear the log as these actually
have the effect of dirtying it in a readonly unmount.


Date:  Tue Jun 10 09:09:42 PDT 2003
Workarea:  jen.americas.sgi.com:/src/lord/xfs-linux.2.4

The following file(s) were checked into:
  bonnie.engr.sgi.com:/isms/slinx/2.4.x-xfs


Modid:  2.4.x-xfs:slinx:150738a
linux/fs/xfs/xfs_log.c - 1.273
        - make xlog_need_covered pay attention to the readonly
          flag.