Randomisations - track the number of ties

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The randomisations currently track the number of times the original result was 
greater than the randomised result.  It also needs to keep a track of the 
number times they were equal.  This is important for two-tailed distributions 
where it is also important to know how often the original was lower.  

If there are ties then the p-values need to be adjusted, but this can be left 
to the user for now.  

Original issue reported on code.google.com by shawnlaffan on 23 Jun 2010 at 3:44