[Sane-analysis] Follow-up on tracking through the reversed target field

[James Maxwell]

> http://twist.phys.virginia.edu/~jdm2z/sane/cross-hair.png

I've re-assessed what I think it might look like to the slow raster
cross-hair plots if the field was reversed.  In the plot I posted
before, I had erroneously positioned the upper crosshair at upstream,
when it was actually downstream.  The beam would be coming at you in
this picture:  http://www.jlab.org/~sanetarget/sane%20pictures/target387.html

I also neglected to show how the beam spot would be skewed to an
ellipse in the plane of the cup lids if it were coming in at angle.
The slow raster plot will still show a circle; the visualization
is a bit clearer in this update:

http://twist.phys.virginia.edu/~jdm2z/sane/cross-hair.png

This 260 degree case is closer in line with what Whit is showing.

Thanks,
James