java plugin: Add support for `match' callbacks.

java plugin: Add support for `match' callbacks.

Holy crap, that one needed some serious magic.. The problem is, that the
filter chains are created before the initialization functions are run.
Since the Java plugin used to initialize the JVM and load the classes in
the init function, the match callbacks were not available in time.

The behavior is now: Create the JVM as soon as the the first `LoadPlugin'
option is found and load and configure all Java plugins while in the
configuration phase. (I. e. exactly like C plugins.)

Phew, I've earned that beer now.