ensure make ptest run MPI programs one after another when users try to run make in parallel

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1635 c368ceb8-fd28-0410-a457-e46ee1d7cd4a
stop trying to build libpnetcdf.a from benchmarks directory

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1636 c368ceb8-fd28-0410-a457-e46ee1d7cd4a
stop trying to build libpnetcdf.a from src/utils directory

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1637 c368ceb8-fd28-0410-a457-e46ee1d7cd4a
un-silence this build command

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1638 c368ceb8-fd28-0410-a457-e46ee1d7cd4a