[rfc] replacing /boot/kernel.old with a unique directory name

hi there,

i just had the following idea: how about instead of copying the current kernel
to /boot/kernel.old and then installing the new one under /boot/kernel as the
results of target installkernel, we create a unique directory name for the old
kernel?

something like /boot/kernel-r${revision}-${/dev/random}?

that would let people not only boot the previous kernel, but all kernels that
have been replaced by target installkernel. this would make tracking issues,
which have been introduced by a certain commit much easier, imho.

i don't think implementing this logic would be that difficult. the only problem
i see is with ${/dev/random} in the case where people are running a kernel
without /dev/{u}random support.

cheers.
alex