PARTIAL TAKE 904029 - Fix process flag handling

[Eric Sandeen <sandeen@xxxxxxxxxxxxxxxxxxxxxxxx>]

We previously had a possibility of corrupting process flags
when restoring saved state from nested PF_FSTRANS settings,
this should fix it up.

Never saw a resulting bug in the wild, but demonstrated
the possibility.

Date:  Mon Mar  8 14:45:20 PST 2004
Workarea:  penguin.americas.sgi.com:/src/eric/xfs-trees/xfs-GUT
Inspected by:  felixb,hch

The following file(s) were checked into:
  bonnie.engr.sgi.com:/isms/xfs-kern/xfs-linux


Modid:  xfs-linux:xfs-kern:168082a
xfs_trans.c - 1.155
        - Use PFLAGS_RESTORE_FSTRANS in place of PFLAGS_RESTORE,
          only restore previously saved FSTRANS state.  Otherwise
          we can lose process flags.

linux-2.4/xfs_aops.c - 1.74
        - Update PFLAGS_SET_NOIO macro, no saved state

linux-2.6/kmem.h - 1.22
        - New PFLAGS_RESTORE_FSTRANS macro to restore only FSTRANS
          state from saved state

linux-2.4/kmem.h - 1.24
        - Simplify PFLAGS_SET_NOIO macros, no need to save state
          New PFLAGS_RESTORE_FSTRANS macro to restore only FSTRANS
          state from saved state