Use Runnable instead of AsyncTask to poll for syncthing web gui (fixes …

…#41).

This works around a  problem with pre-Jellybean devices, where AsyncTask
must be created on the main thread,

src/main/java/com/nutomic/syncthingandroid/WebGuiActivity.java

@@ -99,7 +99,12 @@ public void onCreate(Bundle savedInstanceState) {
 	 */
 	@Override
 	public void onWebGuiAvailable() {
-		mWebView.loadUrl(mSyncthingService.getApi().getUrl());
+		runOnUiThread(new Runnable() {
+			@Override
+			public void run() {
+				mWebView.loadUrl(mSyncthingService.getApi().getUrl());
+			}
+		});
 	}
 
 	@Override

src/main/java/com/nutomic/syncthingandroid/syncthing/SyncthingService.java

@@ -200,9 +200,9 @@ public void run() {
 	 * Polls SYNCTHING_URL until it returns HTTP status OK, then calls all listeners
 	 * in mOnWebGuiAvailableListeners and clears it.
 	 */
-	private class PollWebGuiAvailableTask extends AsyncTask<Void, Void, Void> {
+	private class PollWebGuiAvailableRunnable implements Runnable {
 		@Override
-		protected Void doInBackground(Void... voids) {
+		public void run() {
 			int status = 0;
 			HttpClient httpclient = new DefaultHttpClient();
 			HttpHead head = new HttpHead(mApi.getUrl());
@@ -225,11 +225,7 @@ protected Void doInBackground(Void... voids) {
 					Log.w(TAG, "Failed to poll for web interface", e);
 				}
 			} while(status != HttpStatus.SC_OK);
-			return null;
-		}
 
-		@Override
-		protected void onPostExecute(Void aVoid) {
 			Log.i(TAG, "Web GUI has come online at " + mApi.getUrl());
 			mIsWebGuiAvailable = true;
 			for (OnWebGuiAvailableListener listener : mOnWebGuiAvailableListeners) {
@@ -332,7 +328,7 @@ public void run() {
 					new PostTask().execute(mApi.getUrl(), PostTask.URI_SHUTDOWN, apiKey);
 					registerOnWebGuiAvailableListener(mApi);
 				}
-				new PollWebGuiAvailableTask().execute();
+				new Thread(new PollWebGuiAvailableRunnable()).start();
 				runNative();
 			}
 		}).start();
@@ -362,6 +358,8 @@ public boolean isWebGuiAvailable() {
 	 *
 	 * If the web gui is already available, listener will be called immediately.
 	 * Listeners are unregistered automatically after being called.
+	 *
+	 * Note that the listener might be called on a background thread.
 	 */
 	public void registerOnWebGuiAvailableListener(OnWebGuiAvailableListener listener) {
 		if (mIsWebGuiAvailable) {