[Yaffs] More checkpointing

[Charles Manning]

Over the last few days I've checked in some fixes and tweaks to the 
checkpointing code. The last lot were to fix an issue with freespace getting 
confused by a sync, and some test code to check that an existing partition 
can be upgraded. 

Thanks due to Kent who has been doing or coordinating a lot of the testing and 
has also fixed a few bugs and put forward the qsort stuff.

At this stage I have not updated the make files, because I have been testing 
with a tweaked 2.4 build and yaffs/direct, so you will have to add the new 
files to the build. These are:

yaffs_qsort.c, yaffs_nand.c and yaffs_checkptrw.c 

At this stage, the checkpointing is looking pretty solid and we know of no 
bugs in the checkpointing stuff.

-- CHarles