Application restart introduced.

When processing a restart request, the router sends a QUIT message to all
existing processes of the application.  Then, a new shared application port is
created to ensure that new requests won't be handled by the old processes of
the application.

test/unit/applications/lang/python.py

@@ -44,6 +44,7 @@ class TestApplicationPython(TestApplicationProto):
 
         for attr in (
             'callable',
+            'environment',
             'home',
             'limits',
             'path',