#21 New diagnostics without netcdf

[Edmund Highcock]

Currently the new diagnostics will not build without netcdf (as noted in [bugs:#21]). In release 7.0.x and earlier anyone who wants to use GS2 without netcdf can build with USE_NEW_DIAG undefined and use the old diagnostics. As of 7.1 the old diagnostics will be removed. However, we would like to continue to support GS2 use without netcdf, and it is a set of simple changes to allow this with the new diagnostics.