Bug#481542: grub2: please user triggers

[Felix Zielcke]

retitle 481542 please use triggers for update-grub
thanks

I looked now at the man-db package which is a very easy implementation
for triggers.
I think it would be enough for us to do it like they did.

debian/triggers:
interest /boot

debian/*.postinst:
if [ "$1" = triggered ]; then
  update-grub
fi

>IMHO it's important to consider how triggers would handle a situation
>such as an apt run that removed the running kernel added a new kernel,
>and then failed. In this case, the grub trigger might not run, which
>would leave a menu.lst that contained only a nonexistent kernel.

Well if removing the current installed kernel suceeded, but installing the new one failed,
then I think you don't have any kernel at all in /boot
Removing the current kernel should tell dpkg to run our trigger.
I don't think that if installing a new kernel fails, that the trigger doestn't get called,
as long as the whole install/update apt/dpkg process keeps running
But I try to reproduce this.

Luckly we currently have currently anyway a package in experimental.