fix minitwit/flaskr test errors, improve docs about file open mode

app.open_resource needs to get called with the correct mode param (python3
will read bytes [not str] if the wrong mode is used), add mode param docs.

rv.data is bytes, fix the data type we compare it with to be also bytes

docs/tutorial/dbinit.rst

@@ -33,7 +33,7 @@ earlier.  Just add that function below the `connect_db` function in
 
     def init_db():
         with closing(connect_db()) as db:
-            with app.open_resource('schema.sql') as f:
+            with app.open_resource('schema.sql', mode='r') as f:
                 db.cursor().executescript(f.read())
             db.commit()