Fix test case and Grizzly impl.

Author: rlubke

src/main/java/com/ning/http/client/providers/grizzly/GrizzlyAsyncHttpProvider.java

@@ -200,6 +200,9 @@ public GrizzlyAsyncHttpProvider(final AsyncHttpClientConfig clientConfig) {
     public <T> ListenableFuture<T> execute(final Request request,
                                            final AsyncHandler<T> handler) throws IOException {
 
+        if (clientTransport.isStopped()) {
+            throw new IOException("AsyncHttpClient has been closed.");
+        }
         final ProxyServer proxy = ProxyUtils.getProxyServer(clientConfig, request);
         final GrizzlyResponseFuture<T> future = new GrizzlyResponseFuture<T>(this, request, handler, proxy);
         future.setDelegate(SafeFutureImpl.<T>create());

src/test/java/com/ning/http/client/async/SimpleAsyncHttpClientTest.java

@@ -255,13 +255,6 @@ public void testCloseMasterInvalidDerived() throws Exception {
             fail("Expected closed AHC");
         } catch (IOException e) {
             // expected -- Seems to me that this behavior conflicts with the requirements of Future.get()
-        } catch (ExecutionException ee) {
-            if (!(ee.getCause() instanceof IOException)) {
-                fail("ExecutionException thrown, but the cause was not an instance of IOException.");
-            }
-        } catch (Throwable t) {
-            fail("Unexpected Exception thrown: " + t.toString());
-            t.printStackTrace();
         }
     }