There is also a new API called InvokeEvent.reason. This event is dispatched by the NativeApplication when the application is started from the command line, via the GUI, or by opening an associated file. Applications can register and listen to the InvokeEvent and may also register themselves to launch automatically during user login.
From Robert Christensen:
"You do not need to recompile your application to take advantage of the 1.5.1 improvements. However, if you want to take advantage of the new APIs introduced in this release you will need to update your application descriptor to 1.5.1 (see New APIs section of the release notes) and recompile your application."