device filtering support

[Pete Batard]

On 2012.02.06 00:35, Pete Batard wrote:
> there's about 4 items in there that we can keep in the library (lock,
> refcnt, ctx, possibly session_data) while all the rest can be
> provided/queried from an external source. And I don't really see a major
> obstruction to such a split up at the moment.

Maybe a poor choice of words, so I'll clarify just in case:
Not exactly a split as much as a master version in the enum process and 
a copy in the app. The libusb_device struct would stay pretty much the 
same in the library, bar possibly the list element. But most most of it 
would a copy of data provided by the enum process after query.

Regards,

/Pete