[Yaffs] Some YAFFS2 CVS changes

[Charles Manning]

Hi YAFFSers

I have made a few changes to CVS for YAFFS2:
1) People using yaffs direct with more recent versions of Linux were having 
problems compiling because of issues with the way st_time etc were defined.  
I have changed all the yaffs2 fields from st_xxxx to yst_xxxx to get around 
this.

2) The yaffs2 garbage collector had some issues where it would start to work 
too hard when the partition became full and write would get very slow when 
full. This has been fixed by a better decoupling between the concept of 
"full" and the number of erased blocks. Some testers report that the system 
performance under disk full conditions is very much improved.

-- Charles