core/net/uip: Experimental support for loopback capability.

Enabled via setting UIP_CONF_LOOPBACK_INTERFACE to 1.
avr/usb/rndis: Large refactoring/cleanup.

Removed a lot of jackdaw-specific stuff and made it more flexible.
avr/radio/rf230bb: Cleanup and add hooks.

Removes references to the old rf230 code, which isn't being used
anymore.
nullrdc: Add bridge mode conditions.
cpu/avr/usb/serial: Updates to CDC serial implementation.
Various tweaks to the uip network stack.
Added `*.orig`, `*~`, and `.DS_Store` to `.gitignore`.
platform/avr-ravenusb: Slight improvement to the RNG.
Merge branches 'pull-requests/core-net-uip-loopback', 'pull-requests/cpu-avr-rf230bb-cleanup-hooks', 'pull-requests/cpu-avr-rndis-refactor', 'pull-requests/cpu-avr-usb-cdc-serial-update', 'pull-requests/nullrdc-bridge-mode', 'pull-requests/avr-ravenusb-random-tweak', 'pull-requests/more-gitignore' and 'uip-updates' into bleeding-edge
Merge branch 'pull-requests/platform-avr-ravenusb-leds' into bleeding-edge

Conflicts:
	platform/avr-ravenusb/contiki-conf.h
jackdaw: Move cdc_task and sicslow_ethernet over to ravenusbstick.

The "Jackdaw" firmware for the Atmel RZUSBStick could be very useful
on other platforms, but it's implementation is highly integrated into
the `avr-ravenusb` platform. This commit takes the first step toward
changing that, by moving the cdc_task and sicslow_ethernet code out
of the `avr-ravenusb` platform and into the `ravenusbstick` example.
platform/avr-ravenusb: Added experimental mechanism to switch RDC at runtime.
More updates.
Add configurable PAN ID