* include/grub/i386/linux.h (GRUB_VIDEO_TYPE_TEXT): New macro.
* loader/i386/linux.c [__i386__] (grub_linux_boot): Simplify inline
assembly in final jump, using register constraints.
(grub_linux_boot): For text mode, initialize `have_vga' using
GRUB_VIDEO_TYPE_TEXT rather than 0 (this changes its value to 1).
Initialize `video_cursor_x' and `video_cursor_y' as late as possible,
right before the final jump.
Set `video_mode' to 0x3.
Document initialization of `video_page', `video_mode' and
`video_ega_bx'.