Rome 1.5 retry

Well, after repeatedly shooting myself in the food by trying to run the tests with Java 8 (yields a NoClassDefFound: org.slf4j.LoggerFactory error. Fancy), I seem to have fixed this. 
The dependency from _netcdf_ to _jdom_, which was is declared optional in _netcdf_'s POM was (inadvertendly) satifisfied by _rome_, until _rome_ upgraded to _jdom2_ with the upgrade to _rome_ 1.5. This fix makes _netcdf_'s dependency on _jdom_ (1), which apparently is not optional, explicit and required. Resulting in all tests being green again. I chose this approach over the more aggressive one where _netcdf_ is updated, which would then require the same version of _jdom_ as _rome_ (and then also declares that dependency as non-optional), however I can't predict the impact that upgrade would have. Furthermore, that upgrade adds dependencies to libs not available on sonatype/maven.org.