Bug#502446: update on grub-installer

[Osamu Aoki <osamu@debian.org>]

As I check after good night sleep, I realize my previous patch should
have been not:

+frgrubroot=$(($frbootpart - $grub_part_offset))

but should have been:

+frgrubroot=$(($frgrubroot - $grub_part_offset))

if this should also work for Serial ATA multipath which I do not use.
(RAID should have been OK.)

Other than this, I like Robert Millan's patch and integrated it to mine
which address more issues.

I still think making 30_otheros is ugly hack and if possible should be
replaced with grub's code itself.

After installing os-prober with "apt-install os-prober" , running

$chroot $ROOT update-grub

should create entry but it doesn't as now.  It could likely be
availability of /dev/hd? /dev/sd? etc in chroot.

Osamu

PS: bug in my earlier patch thought was: s/grub_vrsion/grub_version/
+case $grub_vrsion in
+       grub)   frgrubroot=$(($frbootpart - 1)) ;;
+       grub2)  frgrubroot=$frbootpart ;;
+       *)      exit 1 ;;
+esac

This part again hit me when I changed style.