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/patterns/sqlite3.rst

@@ -124,7 +124,7 @@ can do that for you::
     def init_db():
         with app.app_context():
             db = get_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()