TAKE - Un-race-ify timer manipulation in pagebuf

[Eric Sandeen <sandeen@xxxxxxx>]

I don't think we've ever seen problems, but this should be safer.

Use mod_timer in place of del/modify/add (can race)
Also use del_timer_sync when we're done.

Date:  Thu Mar 20 08:07:06 PST 2003
Workarea:  
stout.americas.sgi.com:/localhome/src/sandeen/2.4.x-xfs/workarea-alwaysclean
Author:  sandeen
Merged by:  sandeen
Merged mods:  2.4.x-xfs-dev:slinx:142197a

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


Modid:  2.4.x-xfs:slinx:142197a
linux/fs/xfs/pagebuf/page_buf.c - 1.106
        - Merge of 2.4.x-xfs-dev:slinx:142197a by sandeen.