core/net/sicslowmac: Added support for "bridge mode".

Enabled via setting SICSLOWMAC_CONF_BRIDGE_MODE to 1.
Various tweaks to the uip network stack.
Merge branches 'native-target-osx', 'avr-updates', 'settings', 'mdns-resolv' and 'uip-updates'
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: Move management of LED status to dedicated thread.

This change creates a new thread for managing the LEDs on the Atmel
RZUSBStick hardware. It provides a simple interface for manipulating
the LEDs and makes sure that they are managed in a visually-pleasing
manner, while also providing a hardware abstraction layer.
jackdaw: More work on divorcing Jackdaw from `avr-ravenusb`
Revert "Cleaned up RF230BB, and refactored FRAME_RETRIES and CSMA_RETRIES"

This reverts commit b43dad00b0d598c7ee9f974b4a820a8fe5082d2e.

This change was reverted because it breaks the radio on
the `avr-raven` and `avr-ravenusb` platforms. The exact
cause of this regression has not yet been determined.

Conflicts:

	cpu/avr/radio/rf230bb/rf230bb.c
	platform/avr-ravenusb/contiki-conf.h