halst/schema — pull request #10 by thomaserlang (2013-01-28 20:53:04+00:00)
Title: Fixed wrong error message on optional key dict validate

```Schema({Optional('i'): Use(int)}).validate({'i': 'x'})```

Gave the error:
```wrong keys {} in {'i': 'x'}```

Even if the custom error was set:

```Schema({Optional('i'): Use(int, error='should be a number')}).validate({'i': 'x'})```