We could consider it a goal to change it back to `libusb` if/when Homebrew replaces `libusb` with `libusbx` entirely. Until then, it would be wise to leave it `libusbx` because installing `libusb` caused things not to work for me.

Interestingly enough, `libusbx` wasn't present on my system (OSX 10.9) and the extconf ran, but didn't compile. I must have `libusb` installed through something else, or the extconf didn't fail correctly - I don't think that OSX comes with it.