add VECSUM_SKIP_SUM; set chunk sizes to 4MB
add VECSUM_SKIP_SUM; set chunk sizes to 4MB

Signed-off-by: Colin Patrick McCabe <3142ce8a0bdba4a38073365893e6b74f72d9c512@cloudera.com>

umbrant/caching_benchmarking,umbrant/caching_benchmarking,umbrant/caching_benchmarking,umbrant/caching_benchmarking