Make featureset `__eq__()` more efficient

- Instead of creating a copy with sorted indices, we check whether the indices are already sorted and, if not, we sort them in place. This way, the sorting *only* happens once in the life of a featureset object.
Minor PEP-8 fixes.
Update utils.py

- Remove outdated comments.
- Minor readability fixes.
Fix error printing in test_utilities.py

- Print the captured stderr *after* stdout is released.
Added explicit tests for rescaled regressors

- Added `test_rescaling()` in order to test that rescaling the linear regressors is actually working.
Adddd mock to 2.7 requirements.
Added tests for `summarize_results` and `run_experiment` scripts

- Used mock to test the argument parsing for these scripts since the tests for their actual functionality already exist.