Fix possible memory leak (encountered in h1, see r7255)

* ToeThread.java
    run() - set local variable curi=null when finished with it, because the jvm seems to be holding on to it even after the containing block is finished

engine/src/main/java/org/archive/crawler/framework/ToeThread.java

@@ -187,6 +187,7 @@ implements MultiReporter, ProgressStatisticsReporter,
                     controller.getFrontier().endDisposition();
                     setCurrentCuri(null);
                 }
+                curi = null;
                 
                 setStep(Step.FINISHING_PROCESS, null);
                 lastFinishTime = System.currentTimeMillis();