Fix SelectSelector to be compatible with monkey_patch

[snapiri]

When using eventlet.monkey_patch(), it disables all the Selectors but the SelectSelector. Another thing it does is modify how the constructor handles the class methods. The way the SelectSelector handles the _select function is incompatible with that code. We should have a bound method calling the select function (as is done for the Win32) in order to fix this compatibility issue.

[vstinner]

FYI Trollius is looking for a new maintainer: I don't maintain it anymore.