Clover's Log4J handling is broken

Log4j's interface has changed a bit since we coded support for it. It would work but our initialisation code looks for the wrong method signature

clover.org.apache.log4j.Logger.log(clover.org.apache.log4j.Level, Object, Throwable)

but should be looking for

clover.org.apache.log4j.Category.log(clover.org.apache.log4j.Priority, Object, Throwable)