Make "Found substring" message more explainable e.g. Current month detected

During playing around with mlstats a message appeared in the stdout:

```
Found substring 2014-June in URL http://lists.typo3.org/pipermail/typo3-dev/2014-June.txt.gz...
```

After reading i wasn`t sure what does mean at the first time.
I recognised that this only occurred at the current month. After a look in the source: yep i am right.
To avoid such a feeling for other people i changed the message to something more meaningful:

```
Current month detected: Found substring 2014-June in URL http://lists.typo3.org/pipermail/typo3-dev/2014-June.txt.gz...
```