* Permit nan, inf, and -inf for float SpinBox
Bounds are enforced against inf and -inf inputs, but not for nan.
* Ensure SpinBox text is updated when out-of-bounds value is entered
* Make inf and nan entry in SpinBox case-insensitive
* Make SpinBox example behave as advertised
* Make non-finite SpinBox values optionally allowed
* Python 2 compatibility