Fixed SwingScheduler

[akarnokd]

The SwingScheduler.Worker had bugs and was non-conformant with the expected Worker behavior, which is now fixed:

• Delayed actions were retained after the worker was unsubscribed.
• The non-delayed schedule() call was reentrant and if used for recursive scheduling, a stackoverflow was possible.
• Both delayed and non-delayed actions were added to the tracking composite after they had the chance to run, causing leak of executed tasks.

The new implementation uses a trampoline queue and a fast-path capable drain logic so the EventQueue is not taxed on recursive scheduling.

[epb-644]

Thanks @akarnokd. Maybe we moved too fast on those recent SwingScheduler changes that I made. I might ping you for a review before any future changes, if that's ok.

[akarnokd]

Sure.