Update the quadratic roots example to make sense

 - Mention that it requires the NASA PVS libraries, otherwise a
missing library error is generated.
 - Change the inputs to the roots so that the function has actual
real roots.  Otherwise when you run the simulation there is a difference
generated on x1, and makes the whole thing look broken.


git-svn-id: https://groke.mcmaster.ca/svn/grad/colin/trunk/TableTool@10148 57e6efec-57d4-0310-aeb1-a6c144bb1a8b