This switch is meant to be used by packages requiring an implementation of the
former libusb (as in devel/libusb). The original implementation can be
chosen by setting LIBUSB_TYPE to "native".
The alternative implementation libusb-compat (as in devel/libusb-compat) wraps
libusb1 (in devel/libusb1). This implementation can be chosen by setting
LIBUSB_TYPE to "compat". On NetBSD, it has the advantage of not requiring root
privileges to locate and use USB devices without a kernel driver.
This first part only imports the switch framework itself.
