kernel32/tests: WaitCommEvent may sometimes return immediately on a busy system when write operation to a COM-port has already completed.

It's not enough for some hardware configurations.

kernel32/tests: Accept the case when WriteFile is able to complete the request immediately for an overlapped COM-port write.

The behaviour depends on the driver and hardware used.

This needs to work differently from CorExitProcess because we need to wait for
foreground threads and abort the rest.

Having two instances of Mono loaded at once is problematic, and now that we
use the 2.0 runtime to support 1.x there's no need to support old versions.