[Rd] kendall's tau-b computation (PR#2742)

[dan.field at av.com]

Full_Name: Dan Field
Version: 1.6.2
OS: N/A
Submission from: (NULL) (209.115.168.187)



In kendall.c (library is ctest), the limits for the first loop in routine
kendall_tau run from 0 through n-1, and the inner loop runs from 0 through i-1. 
This causes the each pair at index i to be compared with itself; my
understanding is that there should only be n*(n-1)/2 pairs under consideration
for concordance, discordance, and ties.