Work around prefix trait issues with trailing underscores

Traits interprets [trait names that have trailing underscores as prefix traits](http://docs.enthought.com/traits/traits_user_manual/advanced.html#add-class-trait). PySide and PyQt4 expose the `QWidget.raise()` slot as `QWidget.raise_()` to avoid the keyword conflict. We would like to name the corresponding trait `raise_` as well.

We may need to duplicate the contents of `HasTraits.add_class_trait()` without the prefix-trait handling in order to accomplish this.

Start with HasTraits.add_class_trait() and review how trailing underscores are interpreted as prefix traits. Compare that behavior with the QWidget.raise_() naming exposed by PySide and PyQt4. Done means a corresponding raise_ trait can be defined without unwanted prefix-trait handling, with the existing trait behavior preserved.

Written by the indexing model from the issue text.