Implement squashfs with RAM overlay, i.e. using tmpfs instead
of jffs2 as backing store.
Make jffs2 kernel configuration/modules, tools, etc. depend on
the actual jffs2 specific images.
This allows us to use 5*64 KiB = 320 KiB – or, depending on the
model's flash block size, even 5*128 KiB = 640 KiB – more flash
space (jffs2 requires 5 free blocks to work, I don't know why,
and this sucks), plus the blocks actually used by the data stored
on jffs2, plus the size gained by reducing the tools and modules
in the image. Changes would of course be lost on reboot (except
these in /etc), but there's always external storage (or put stuff
into fwcf and have /etc/rc.local symlink from there), and we can
pack more stuff into the images.
