Bug#707653: Grub 2.00-14 upgrade from 1.99 failed to run update-grub

[Uoti Urpala]

I encountered this bug, though the system still booted successfully with
some error messages.

"grub-install /dev/sda" and "update-grub" fixed the problem.

'dpkg-reconfigure grub-pc' was NOT useful.

I think grub-pc.postinst failed to run any of the code paths that would
run update-grub. The script seems to use existence of "stage2" file as a
trigger for update path from legacy grub and existence of "core.img" as
a trigger for new grub. Before running the above commands, my system had
neither a file named "stage2" nor one named "core.img", so the script
did nothing.