Pin correct names to wrapped Index comparison methods
Currently:
```
>>> pd.Index.__eq__.__name__
'_evaluate_compare'
```

PR:
```
>>> pd.Index.__eq__.__name__
'__eq__'
```

Same for subclasses and other comparison methods.

On the side: use property decorator for `DatetimeIndex.freq` to avoid leaving `_get_freq` and `_set_freq` in the namespace.

- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
