If the class is already set in the classes map in PluginClassLoader, check if it's set to something different to what we were setting it to before spamming console with non-errors.

Signed-off-by: Ross Allan <rallanpcl@gmail.com>
Merge pull request #825 from nallar/MC147

If the class is already set in the classes map in PluginClassLoader, check if it's set to something different to what we were setting it to before spamming console with non-errors.