Startup code should honor shutdown flag more efficiently

[Fred Drake]

The startup code in zope.app.server.main.setup() doesn't consider the possibility that the database opened event might trigger application code that wants to stop the server. The exit_status flag should be checked after any operation in setup that might trigger application code. In particular, the servers should not be started if exit_status has been set. (Even opening the databases might cause a shutdown request.)

For example, a generation that fails and can't allow the database to be used for normal request processing may want to shutdown; it should be able to use zope.app.applicationcontrol.interfaces.IServerControl.shutdown(0) to cancel the startup. By calling shutdown(0) and then sys.exit(), the generation will be cancelled and, eventually, the process will exit.

[Christian Theune (ctheune)]

Sounds like a good idea to me.