Evaluate all p: tags when cleaning them

Don't just consider the first p tag value in a todo item, consider all
of them.

test/test_todo_list.py

@@ -420,5 +420,19 @@ class TodoListCleanDependencyTester(TopydoTest):
 
         self.assertFalse(self.todolist.todo(1).has_tag('id'))
 
+    def test_clean_dependencies4(self):
+        """ Clean p: items when siblings are still connected to parent. """
+        self.todolist.add("Foo id:1")
+        self.todolist.add("Bar p:1")
+        self.todolist.add("Baz p:1 id:2")
+        self.todolist.add("Buzz p:2 p:1")
+
+        self.todolist.clean_dependencies()
+
+        self.assertFalse(self.todolist.todo(4).has_tag('p', '1'))
+        self.assertTrue(self.todolist.todo(1).has_tag('id', '1'))
+        self.assertTrue(self.todolist.todo(2).has_tag('p', '1'))
+
+
 if __name__ == '__main__':
     unittest.main()

topydo/lib/TodoList.py

@@ -227,11 +227,11 @@ class TodoList(TodoListBase):
             """
 
             for todo in [todo for todo in self._todos if todo.has_tag('p')]:
-                value = todo.tag_value('p')
-                parent = self.todo_by_dep_id(value)
+                for value in todo.tag_values('p'):
+                    parent = self.todo_by_dep_id(value)
 
-                if not self._depgraph.has_edge(hash(parent), hash(todo)):
-                    remove_tag(todo, 'p', value)
+                    if not self._depgraph.has_edge(hash(parent), hash(todo)):
+                        remove_tag(todo, 'p', value)
 
         self._depgraph.transitively_reduce()
         clean_parent_relations()