Core: Fix unconditional disarming of timerfd

* Existing code appears disarms the timerfd always, which cancels
  pending timeouts as soon as one packet completes.
* This fix moves the disarming of the timerfd to
  arm_timerfd_for_next_timeout(), where it is now done conditionally.
  It also avoids calling disarm outside of the above call.
* This patch also ensures that all handling of the timerfd is done
  under the flying transfers lock.
* Issue reported by Hans de Goede. For more info, see:
  https://sourceforge.net/mailarchive/message.php?msg_id=29442693

Conflicts:
	libusb/io.c
	libusb/version_nano.h
Linux: Return ERROR_NOT_FOUND in detach-kernel-driver if usbfs is already bound

* Currently applications for devices which only are accessed from userspace
  can use claim / release interface to make sure they don't get in each others
  way.
* The same however does not work for applications which first need to detach
  a "native" / in kernel driver, as this detach will not only detach native
  drivers but also the usbfs driver, thus stealing the device from another
  userspace / libusbx app.
* This patch fixes libusb_detach_kernel_driver to only detach "real" kernel
  drivers and not the special usbfs driver used for userspace access to
  USB devices. If the usbfs driver is found LIBUSB_ERROR_NOT_FOUND will be
  returned to indicate no driver was detached.

Conflicts:
	libusb/version_nano.h
All: Avoid polluting errors reported on device disconnect

* Makes libusb_cancel_transfer not log an error when the cancel fails
  with LIBUSB_ERROR_NO_DEVICE, so that apps can properly clean things
  up on device disconnect without flooding the console with these errors.
* Also, some devices (Cypress FX) may switch VID:PID on the fly during
  firmware upload => reduce severity of the Windows message when that happens.

Conflicts:
	libusb/os/windows_usb.c
	libusb/version_nano.h