How to upgrade chain-booted grub-pc?

[Mike Bird <mgb-debian@yosemite.net>]

A dist-upgrade to Squeeze results in a chain boot
comprising both grub1 (grub-pc) and grub2.

Today's grub-pc update now wants to know where to
automatically install, presumably because it does
not recognize grub2's chain-boot setup.

Unfortunately, I also don't know the details of
what grub2 did to make the chain boot, so I don't
know what to tell grub1 (grub-pc) when it asks:

"The grub-pc package is being upgraded. This menu
allows you to select which devices you'd like
grub-install to be automatically run for, if any."

Does anyone have any solid recommendations (no
wild guesses please) as to how to determine the
best response?

Thanks,

--Mike Bird