Add configure option to bypass boot menu if possible

Add configure option to bypass boot menu if possible

If other operating systems are installed, then automatically unhide the
menu.  Otherwise, if GRUB_HIDDEN_TIMEOUT is 0, then use keystatus if
available to check whether Shift is pressed.  If it is, show the menu,
otherwise boot immediately.  If keystatus is not available, then fall
back to a short delay interruptible with Escape.

This may or may not remain Ubuntu-specific, although it's not obviously
wanted upstream.  It implements a requirement of
https://wiki.ubuntu.com/DesktopExperienceTeam/KarmicBootExperienceDesignSpec#Bootloader.

If the previous boot failed (defined as failing to get to the end of one
of the normal runlevels), then show the boot menu regardless.

Author: Richard Laager <rlaager@wiktel.com>
Author: Robie Basak <robie.basak@ubuntu.com>
Forwarded: no
Last-Update: 2015-09-04

Patch-Name: quick_boot.patch