Fix #238 - Allow to skip scenario in step function

This pull request contains a feature file that exibits the case of one scenario skipped out of 2, and of course, the small patch to fix it.

It also contains two minor fixes that I found while I tried to use python3.3. Those fixes are compatible with python2.7 but untested on python 2.[4-6]. Those concerned might want to check that:

```python
"KEY" in os.environ
```
behave as
```python
os.environ.has_key("KEY")
```
and that
```python
ConfigParser.get('section', 'key', raw = True)
```
behave as
```python
ConfigParser.get('section', 'key', True)
```