java plugin: Use the changed plugin infrastructure to call read and write functions...

java plugin: Use the changed plugin infrastructure to call read and write functions directly.

The read and write functions implemented in Java are now registered with
the "complex" interface as "java:<class name>". This way the cjni_read and
cjni_write functions can determine which Java function to call.

The patch is bigger than it'd need to be, because the order of some
functions has been changed..