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.
experimental change to multiloc
Merge remote-tracking branch 'mark/ground' into ground
intermediate state needing more work
Fixes bug with GoOut action

The GoOut action was producing a run-time error since it was trying
to refer to a non-existent dirProd of the current command object.
Since GoOut (triggered by LEAVE or EXIT) already implies outDir,
it doesn't need to look at dirProd.
Hopefully fixed MultiLoc

The problem was that the locationList property of MultiLoc was being used
for two incompatible purposes: maintaining a current list of rooms and
Things in which the MultiLoc is currently located, and defining a list
of Rooms, Things and *Regions* in which the MultiLoc is meant to start
out. This fix introduces an initialLocationList property for the
second purpose, and copies the locationProperty to it if it looks like
the user has defined that instead.
Merge branch 'multiloc' into ground
Alternative implentation of Ground

This defines a Floor class much like Mark's DefaultGround, but
defines the behaviour on the class. It then defines a defaultGround
object of the Floor class, which by default is added to every
Room (although this can be customized). The vocab for the
defaultGround object is defined in english.t.