Correlated t-test for paritioned GLS
part_ttest(coefs, part.covar_coef, rcoefficients, df2, npart)
a list whose first element is a coefficient table with estimates, standard errors, t-statistics, and p-values and whose second element is a matrix of correlations among coefficients.
vector average GLS coefficients
an array of covar_coef from each partition
an rcoefficeints array, one for each partition
second degree of freedom from partitioned GLS
number of partitions