Mouse jumps to left in Xorg

[Justin Hibbits]

When I move the mouse over some threshold, it gets locked to either the left or
the top of the screen in X.  Killing X fixes this, and I'm able to move the
mouse slowly around the screen, but moving it at a "normal" rate after it gets
stuck warps it back to its stuck side.

I've googled for solutions to this, and it appears the problem is that the FPU
state isn't saved and/or restored correctly when entering/leaving the signal
handler for SIGIO.  Reading through the code in powerpc/aim/machdep.c, line 498
contains the comments:

    /*
	 * Save the floating-point state, if necessary, then copy it.
	 */
    /* XXX */

which I assume means it's to be done.  I don't know the signal handler code well
enough to implement this, but I can test any patch for this.

- Justin