Fix issue bbangert#180 - KeyError when loading deleted session

Session.load does not properly handle state after .delete and .save was called.

This happens when user logs out, but saves session id, and then tries to use it again.

beaker/session.py

@@ -437,6 +437,7 @@ def load(self):
                 self.is_new = True
 
             if self.timeout is not None and \
+               '_accessed_time' in session_data and \
                now - session_data['_accessed_time'] > self.timeout:
                 timed_out = True
             else:

tests/test_session.py

@@ -483,6 +483,16 @@ def test_invalidate_invalid_signed_cookie_invalidate_corrupt():
     assert "foo" not in dict(session)
 
 
+def test_load_deleted_from_storage_session__not_loaded():
+    req = {'cookie': {'beaker.session.id': 123}}
+    session = Session(req, timeout=1)
+
+    session.delete()
+    session.save()
+
+    Session(req, timeout=1)
+
+
 class TestSaveAccessedTime(unittest.TestCase):
     # These tests can't use the memory session type since it seems that loading
     # winds up with references to the underlying storage and makes changes to