Two zero-distance points annihilate each other

[GoogleCodeExporter]

pbourke discovered that if you have pt 1 & 2 down and bring them close 
together, they merge into one point, and then MTVisualizer thinks there are 0 
points down (you can keep moving pts 1 & 2 and the screen looks like no points 
are down).

Original issue reported on code.google.com by luke.hutch on 22 Apr 2012 at 4:47