Don't try to open the libusb.so which is a linker script in Gentoo and
go straight for the actual libusb-0.1.so.4

http://bugs.gentoo.org/486640

--- tools/nut-scanner/scan_usb.c
+++ tools/nut-scanner/scan_usb.c
@@ -28,7 +28,7 @@
 #include <ltdl.h>
 
 /* dynamic link library stuff */
-static char * libname = "libusb";
+static char * libname = "libusb-0.1";
 static lt_dlhandle dl_handle = NULL;
 static const char *dl_error = NULL;
 static int (*nut_usb_close)(usb_dev_handle *dev);