Bug#564928: the mbr needs updating

[Dennis 123321]

@Felix

You said to run `sudo dpkg-reconfigure grub-pc' as the proper fix; Can
I get this to install to a partition instead? I have a Macbook Pro 13"
(5,5) and using legacy BIOS emulation boot /dev/sda3 (which contains
grub-pc manually installed)/
Running your command, I only get the choice of /dev/sda which is not
appropriate for the Macbook partition scheme.