Fix default no-op lamda to have correct number of params.

Fix for this (Python 2.7.5, FreeBSD 9.1):

```
Traceback (most recent call last):
  File "./manage.py", line 8, in <module>
    from vlasisku import app
  File "/export/home/ders/code/vlasisku/vlasisku/__init__.py", line 10, in <module>
    database.init_app(app)
  File "/export/home/ders/code/vlasisku/vlasisku/database.py", line 138, in init_app
    root = self._load_from_source(cache_path)
  File "/export/home/ders/code/vlasisku/vlasisku/database.py", line 162, in _load_from_source
    root = Root(self)
  File "/export/home/ders/code/vlasisku/vlasisku/database.py", line 217, in __init__
    self._load_entries(xml)
  File "/export/home/ders/code/vlasisku/vlasisku/database.py", line 419, in _load_entries
    processors.get(tag, lambda: None)(entry, text)
TypeError: <lambda>() takes no arguments (2 given)
```