Resolves issue 290: InAppBrowser will not destroy WebView after being closed (by invoking ref.close()) causing memory leaks

src/android/InAppBrowser.java

@@ -536,6 +536,14 @@ public class InAppBrowser extends CordovaPlugin {
                             dialog.dismiss();
                             dialog = null;
                         }
+
+                        if (url.equals(new String("about:blank"))) {
+                            inAppWebView.onPause();
+                            inAppWebView.removeAllViews();
+                            inAppWebView.destroyDrawingCache();
+                            inAppWebView.destroy();
+                            inAppWebView = null;
+                        }
                     }
                 });
                 // NB: From SDK 19: "If you call methods on WebView from any thread