add test cases of the angle difference

[cpanse]

problem recmap (<0.5.29):

bugfix

        if ((gammaM < 0 && gammaC > 0) || ( gammaM > 0 && gammaC < 0))
          delta = fabs(gammaC + gammaM) / C.size();
        else
          delta = fabs(gammaC - gammaM) / C.size();

testthat

R> set.seed(1); (sapply(1:10, function(i){summary(recmap(checkerboard(8)[sample(64,64),]))[4,]}))
 [1] 0.25 0.23 0.11 0.18 0.26 0.24 0.28 0.30 0.34 0.25