Fix setEmissionWave() call by using rdouble rather than rfloat()

As shown by http://ci.openmicroscopy.org/job/OMERO-5.1-merge-training/7/console, the implementation of `setEmissionWave()` on the 5.1.x line from https://github.com/openmicroscopy/openmicroscopy/pull/2377 fails. This PR should fix the training examples.

To test this PR, check http://ci.openmicroscopy.org/job/OMERO-5.1-merge-training/ becomes green again.

--no-rebase