[Nut-upsdev] checking for libusb in configure.in

[Charles Lepple]

Peter,

similar to the OpenSSL test and "with_ssl", can we make the libusb
test in configure.in depend on "with_usb=yes"?

It's not as important as not linking against OpenSSL unless requested,
but it caused a bit of confusion when I was trying to rebuild. I
forgot that "--with-drivers=all" does not imply "--with-usb", and it
was not registering that the libusb checks might be called regardless
of whether --with-usb was set.

I will do the testing and such, but I wanted to ask you before I work
on a patch (especially since there is that "innocent until proven
guilty" comment in there).

-- 
- Charles Lepple