Fix #131 again

Simplified the validation and fixed the problem mentioned in #131 with only the last field in a fieldset being validated.
![131-2-01](https://cloud.githubusercontent.com/assets/7405322/3879636/003969d0-217b-11e4-9ef4-feaf4ef3540c.png)
![131-2-02](https://cloud.githubusercontent.com/assets/7405322/3879637/003f7d70-217b-11e4-9020-533e1d94fc7f.png)

@kgiszewski please pay attention to these comment lines... there's a potential problem here. might need to be solved later on.