Jni update

Java bindings using JNI can now be built using scons. This should work for versions up through Java 9. Scons relies on the javah command to generate C headers for JNI. From Java 10 onward the javah command has been replaced by java -h, so further work will be needed to support later java versions.

Several of the newer combinators have been added to the bindings, but there are still some outstanding.