Minor changes to three extras.t classes

StairwayUp, StairwayDown and Passage now respect the values of the
isClimbable, isClimbDownable and isGoThroughable properties
respectively. Previously the verify() methods for the corresponding
actions on these classes simply ignored these properties and
did nothing.
Version 0.4 release

The changes in this commit simply insert the correct release date
into the title page and changelog page of the manual.