Bug#775317: Depreciated kernel graphics params

[jnqnfe <jnqnfe@gmail.com>]

Control: retitle -1 Use of depreciated graphics param with grub2

To reclarify the problem, now that I have investigated and solved it in
live-build: I noticed a message from grub2 about VGA=788 being a
depreciated graphics param, and being relatively new to linux I
mistakenly thought this was a kernel change which only grub2 was
displaying a message about but which applied to all bootloaders. Now I
have learnt that this isn't a true kernel param, it's used by the
bootloader, and it is simply that grub2 has a new way for users to
express graphics properties.

So, a fix is desirable to provide grub2 with graphics properties via the
new 'set gfxpayload' method.