Added -t4 to standard test parameters, to ensure that thread parallelization does not break correctness. 'omppgi' currently fails the test (but 'ompgnu' passes).
Modified program output to display the actual number of threads (omp_size) instead of the user-requested number (num_threads), because the latter is ignored when OpenMP is disabled. Please note that the output now says '0' threads when OMP is disabled.
Added an OpenMP scaling test.