The reasons for my proposal are:

* It looks awkward to have extra parameter `$encodeSpaces` in `renderSelectOptions()`. But this is no big deal.
* You may still want to configure individual options to have different `$encodeSpaces` settings. This may be specified via `$options['options']`.

It's fine that `dropDownList()` and `listBox()` unset `encodeSpaces`.

Also, I think perhaps we should change the default behavior to be not encoding spaces.