framework, tests: Correct signal disconnection

While the Louie system operated on weakrefs for the callback
functions, the priority list wrapper did not. This difference led to
weakrefs to callback functions being compared to strong references in
list element operations within Louie's disconnect method, so that
handler methods were not disconnected from signals.

Converting the receiver to a weakref then allowed Louie to operate as
normal, which may include deleting and re-appending the handler method
to the receivers list. As ``append`` is a dummy method that allows the
priority list implementation, the handler method is then never added
back to the list of connected functions, so we must ``add`` it after
``connect`` is called.

Also included is a testcase to confirm the proper disconnection of
signals.

tests/test_signal.py

@@ -30,6 +30,27 @@ class Callable(object):
         return self.val
 
 
+class TestSignalDisconnect(unittest.TestCase):
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.callback_ctr = 0
+
+    def setUp(self):
+        signal.connect(self._call_me_once, 'first')
+        signal.connect(self._call_me_once, 'second')
+
+    def test_handler_disconnected(self):
+        signal.send('first')
+        signal.send('second')
+
+    def _call_me_once(self):
+        assert_equal(self.callback_ctr, 0)
+        self.callback_ctr += 1
+        signal.disconnect(self._call_me_once, 'first')
+        signal.disconnect(self._call_me_once, 'second')
+
+
 class TestPriorityDispatcher(unittest.TestCase):
 
     def setUp(self):
@@ -61,12 +82,16 @@ class TestPriorityDispatcher(unittest.TestCase):
 
     def test_wrap_propagate(self):
         d = {'before': False, 'after': False, 'success': False}
+
         def before():
             d['before'] = True
+
         def after():
             d['after'] = True
+
         def success():
             d['success'] = True
+
         signal.connect(before, signal.BEFORE_WORKLOAD_SETUP)
         signal.connect(after, signal.AFTER_WORKLOAD_SETUP)
         signal.connect(success, signal.SUCCESSFUL_WORKLOAD_SETUP)
@@ -76,7 +101,7 @@ class TestPriorityDispatcher(unittest.TestCase):
             with signal.wrap('WORKLOAD_SETUP'):
                 raise RuntimeError()
         except RuntimeError:
-            caught=True
+            caught = True
 
         assert_true(d['before'])
         assert_true(d['after'])