#1 midishare memory leak

[Dominique Fober]

one midishare event is lost per midiopen/midiclose sequence on
client slide: the reason is that the client thread is most of the time
cancelled while waiting on new events (MidigetCommand() ->
MidiGetEvAux()) and that 1 event is used for the communication
with the kernel.
The solution is probably to send an event from server back to
client to exit the client thread in a clean way.