observer: Coerce scalar values in keys to sets

Unfortunately, strings are iterable in python, so without this a call with a
single string, or a construct of "('foo')" would result in creating keys for
each letter of the string 'foo'. "('foo',)" works, because , creates the tuple,
not the parens...

g13gui/g13gui/observer/observer.py

@@ -11,6 +11,8 @@ class Observer(object):
     def _makeChangeTriggerKeys(self, changeType, keys):
         result = []
         if keys != Subject.AllKeys:
+            if type(keys) != set:
+                keys = {keys}
             for key in keys:
                 result.append((changeType, key))
         else: