Fixed the console sigint deadlock, by queuing execution in the finalizer thread.

Fixed the console sigint deadlock, by queuing execution in the finalizer thread.

* console-io.h, console-null.c, console-unix.c, console-win32.c,
gc.c: instead of executing tons of managed code in signal context,
we wake up the finalizer thread and any complex console-specific
code will be handled there. This can cause a (usually small) delay,
but it's much better than deadlocking.