nbininv.m: Increase speed (85X) and accuracy of function (bug #34363). * nbininv.m: Call new function scalar_nbininv to calculate nbininv for scalar. If there are still uncalculated values then call bin_search_nbininv. Call bin_search_nbininv directly for vectors. Add more BIST tests. * nbininv.m (scalar_binoinv): New subfunction to calculate nbininv for scalar x. Stops when x > 1000. * nbininv.m (bin_search_nbininv): New subfunction to do binary search for nbininv.

gnulib-hg = gnulib-hg