Kernels being uninstalled automatically

[Jeff Vian]

I just noticed that when I do an update that includes a kernel the 2nd
older kernel is uninstalled.

For example, right now the new one being installed is 1996 and the one
it is replacing is 1977.  The update is uninstalling the 1969 kernel for
me.

Is that deliberate?
I assume so, but want to be able to NOT have it happen if I choose to
keep the older kernels for whatever reason.

This policy only keeps 2 kernel versions around, and can break a system
if the latest (before the update) had problems for a user and an earlier
version is in use.

How do I turn that off?  
How would I change the number of older kernels to keep around?

Jeff