Windows: Filter out non-libusb I/O completions

Windows: Filter out non-libusb I/O completions

The I/O completion port thread gets notified of every I/O operation that
completes for a given HANDLE, but not all I/O operations originate from
within libusb. For example, libusbK performs a number of I/O control
calls during initialization and specific device operations, such as
setting an interface alternate setting. These non-libusb operations need
to be ignored as the OVERLAPPED associated with such operations is not
tied to a libusb_transfer structure.

Resolve this situation by using the libusb device handle as the I/O
completion port's unique key and keeping a list of active transfers for
each device handle. When the I/O competion port thread is notified of an
I/O completion, it will first match the OVERLAPPED to an outstanding
transfer before acting on it.

Closes #844

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>