rewrite to libusb 1.0 API to work on Mac OS X and add kernel detach

This branch makes a number of changes which I would propose as being version 0.4. 

It adds a codeless kernel extension which can be installed on MacOS X to prevent the kernel driver from grabbing the interface. It also incorporates the check of an active kernel driver using libusb for other platforms. 

The lowlevel.c has been rewritten to use the 1.0 API, rather than the 0.1 API. 

SConstruct file updated to point to the proper libraries installed by brew on MacOS X. 

It has only been tested for fwflash, so likely could use more extensive testing.