grub_machine_fini

["Yoshinori K. Okuji" <okuji@enbug.org>]

I added a new function grub_machine_fini which is an arch-specific 
function. This function is not called automatically, and used only for 
grub-emu at the moment. I implemented this function for grub-emu and 
PC.

This function should be implemented for all architectures, and should be 
called before GRUB exits. I think it is unnecessary to call this 
function from reboot or halt, because the machine should be reset 
completely in this case. So this should be called maybe only from boot.

BTW, I disabled SIGINT in grub-emu, because I wanted to let grub-emu 
catch C-c. When you want to quit grub-emu, you can use halt or reboot 
(or C-\).

Okuji