try to shutdown at the end of every notebook run

this line causes noise in the test suite, but if we just ignore it,
we'll never get to the bottom of it. It seems to only happen when
running 'iptest js', and *not* when running the 'casperjs test' command
directly, with a notebookserver that was launched manually.

IPython/html/tests/casperjs/util.js

@@ -54,7 +54,7 @@ casper.notebook_test = function(test) {
     //XXX: we get sporadic error messages when shutting down some of the tests.
     //     Since the entire server will go down at the end of running the test
     //     suite, it's ok for now to not try to shut anything down.
-    //this.shutdown_current_kernel();
+    this.shutdown_current_kernel();
     
     //XXX: the implementation of delete_current_notebook is currently broken
     //     it's not a big deal, since the notebook directory will be deleted on