Add 'enable-parallel-with-hdf5' option for netcdf

NetCDF library implements parallel I/O through parallel-netcdf (in classic model) or hdf5 (in netcdf4 model). Because parallel-netcdf formula is not formally in Homebrew (https://github.com/mxcl/homebrew/pull/16394), I added an option as in title for compiling parallel I/O for netcdf through hdf5.