SGRefObjects not allowed to share RefCount object any more.
Fixed unit test; moved threaded stress_test fo RefCount_unittest.
Parallel and SGIO should not copy ref-count values with copy-constructor;
rather maintain ref-counts on their own.
Removing obsolete test helper stress_test() - which is now in RefCount_unittest.
C4.5 algorithm added
Removing old protobuf files before starting a new build.
reduced accuracy in kernel row_col_wise_sum_block_with_diag unit-test to prevent buildbot failure
made changes