[Yaffs] Flush cache on umount

[Charles Manning]

Hi YAFFSers

Some people (thanx Michael) found that under certain conditions, files were 
not being flushed correctly on unmount.

Now I always assumed that the Linux VFS would be closing all handles before 
closing a filesystem, but on further inspection this is not the case (at 
least in 2.4 anyway).

Solution: Flush out the YAFFS cache as part of yaffs_put_super (called during 
umount).

This has been lightly tested and is in CVS.

http://www.aleph1.co.uk/cgi-bin/viewcvs.cgi/yaffs2/yaffs_fs.c?r1=1.42&r2=1.43
http://www.aleph1.co.uk/cgi-bin/viewcvs.cgi/yaffs2/yaffs_guts.c?r1=1.30&r2=1.31

-- Charles