Hi, all

The attached patch implements saving of yaffs checkpoint in case fs is
remounted read-only. This allows the usage of checkpoint mechanizm even if,
for some reason, the system can not cleanly unmount yaffs filesystem but can
remount it read-only.

It also fixes a problem with an implementation of yaffs_put_super that
"puts" mtd device before saving yaffs checkpoint.

M.