device filtering support

[Michael Plante]

Pete Batard wrote:
>> we may have to spawn a standalone process

Let's try to avoid this, if we can, regardless of the reason (hotplug,
filtering, or some completely unrelated reason that comes up in a year).
That is very heavy-weight and I think against the philosophy of libusb;
threads I can accept, processes not so much.  Putting on my Windows end-user
hat, I hate having to decide whether to kill processes or not.  If we wind
up duplicating effort within each libusb-using process on each hotplug
event, that seems a fair trade to me, and it sounds to me like you're saying
it's still better than a full enum.


Thanks,
Michael