Summary: Partial rollback changes for 6567564 in the Component.getGC method
Reviewed-by: art, son

Summary: mainAppContext, isDisposed, and numAppContexts has beem made volatile.  mostRecentThreadAppContext has been rewritten using ThreadLocal.
Reviewed-by: art

Summary: Added synchronization to AppContext.getAppContexts()
Reviewed-by: art

Summary: double-check has been removed
Reviewed-by: dav

Summary: SystemFlavorMap is lazily initialized now.
Reviewed-by: uta

Summary: AppContext.dispose() should be ready to get exceptions during disposal of toplevels.  Also now we mark windows peers as destroyed when native object has been destroyed.
Reviewed-by: art

Summary: WindowDisposerRecord should not keep strong reference to AppContext.
Reviewed-by: art