the fact that the `extra_options` is no longer provided when parsing the easyconfig file is an issue, yielding problems like:

```
Traceback (most recent call last):
  File "<string>", line 1, in innertest
  File "/Users/kehoste/TMP/easybuild-easyconfigs/test/easyconfigs/easyconfigs.py", line 218, in template_easyconfig_test
    app = app_class(ec)
  File "/Users/kehoste/work/easybuild-easyblocks/easybuild/easyblocks/s/slepc.py", line 51, in __init__
    if self.cfg['sourceinstall']:
  File "/Users/kehoste/work/easybuild-framework/easybuild/framework/easyconfig/easyconfig.py", line 604, in __getitem__
    value = self._config[key][0]
KeyError: 'sourceinstall'
```

So, to parse the easyconfig, we need an instance of the EasyBlock so we can figure out the extra easyconfig parameters available for that specific easyblock...

I knew this was too easy... :(