Add a feature to display fullscreen help via menu selection entry
(inspired by the Debian install disc menus.)

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

As reported by hpa, strlcpy is safer and could prevent some bugs.
So I replaced all strncpy by strlcpy calls.

The normal behavior for a hotkey is to jump to a specific menu entry.
With MENU IMMEDIATE, it activates the menu entry as well.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

-Werror cleanup.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

Add MENU CLEAR to clear the screen on menu exit.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Clear away the countdown message before actually running the final
boot.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Don't display the cursor on the graphical screen while doing a quiet
boot.  When doing a quiet boot we will probably show the graphical
screen for a fair bit of time; as a result, we really don't want a
completely bogus cursor blob on the bottom of the screen.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Add a MENU RESOLUTION command to make it possible to set a nonstandard
resolution.  If the nonstandard resolution is unavailable, we revert
to the text mode screen.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Add (disabled) debugging hooks to the menu system.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>