support timedelta for SEND_FILE_MAX_AGE_DEFAULT config variable

tests/test_config.py

@@ -10,6 +10,7 @@
 import pytest
 
 import os
+from datetime import timedelta
 import flask
 
 
@@ -168,6 +169,14 @@ def test_session_lifetime():
     assert app.permanent_session_lifetime.seconds == 42
 
 
+def test_send_file_max_age():
+    app = flask.Flask(__name__)
+    app.config['SEND_FILE_MAX_AGE_DEFAULT'] = 3600
+    assert app.send_file_max_age_default.seconds == 3600
+    app.config['SEND_FILE_MAX_AGE_DEFAULT'] = timedelta(hours=2)
+    assert app.send_file_max_age_default.seconds == 7200
+
+
 def test_get_namespace():
     app = flask.Flask(__name__)
     app.config['FOO_OPTION_1'] = 'foo option 1'