Fixed -objectValue in demo, -keyDown, builds in Xcode 4.

* Fixed documentation (in this file) and demo project to reflect the
fact that setting the objectValue of RPTokenControl to a set of
RPCountedToken objects
is no longer supported.

* In demo project Build Settings, updated Build Settings to work in
Xcode 4.   Base SDK is now "Latest Mac OS X", Architectures are now
Xcode default instead
of ppc + i386.

* -[RPTokenControl keyDown:] now forwards un-handled 'tab' key down
events to super, as is proper.