java: Fix generated functions that return RHashtable.

java: Fix generated functions that return RHashtable.

Creating a HashMap directly from JNI is possible but very tedious
(see: http://java.sun.com/docs/books/jni/html/fldmeth.html#26254)

Instead we use the existing code to return hashes from JNI as plain
String[], then add some code in the Java wrapper to convert these to
HashMap<String,String>.
(cherry picked from commit eb54a7ede43d9275f10db6fce1472256550da0eb)