- Move the mouse cursor to the center of the screen after video

- Move the mouse cursor to the center of the screen after video
mode switch in ioctl.
Possibly related to PR: kern/4271

- A kludge: initialize scp->xpixel and ypixel even in the text mode.
If the console enters the `unknown' graphics mode via the ioctl KDSETMODE
(KD_GRAPHICS), these fields are not set (because syscons cannot know
the correct values), but set_mouse_pos() need to refer to these field
to adjust the mouse position.

- Turn off MOUSE_VISIBLE when switching video mode by ioctl.

- another new option: SC_MOUSE_CHAR
Define the first character code of four consecutive codes to be used for
the mouse cursor.  Default codes are 0xd0 through 0xd3.  Beware that
if you decide to use any codes outside the range of 0xc0-0xdf,
the mouse cursor may not look good, because of the way VGA displays
characters in 9-dot-wide character cells.
Requested by several people.

(This patch was tested by a person who recently reported, in the -current
ML, a page fault problem in the kernel (draw_mouse_iamge()) after
X server shutdown. The patch cured his problem.)