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

"Bridge mode" allows devices to more easily send 802.15.4 packets as if
they were a different device. It also turns off any packet filtering
that may be implemented at layer 2. It works by allowing
`PACKETBUF_ADDR_SENDER` to be set earlier in the stack.

This is useful for implementing 6LoWPAN-ethernet bridges.

Enabled via setting `NETSTACK_CONF_MAC_BRIDGE_MODE` to 1. Disabled by
default.
core/net/uip: Experimental support for loopback capability.

Enabled via setting UIP_CONF_LOOPBACK_INTERFACE to 1.
cpu/avr: Added "AVRDUDE_MCU" configuration parameter.
avr/radio/rf230bb: Cleanup and add hooks.

Removes references to the old rf230 code, which isn't being used
anymore.
avr/usb/rndis: Large refactoring/cleanup.

Removed a lot of jackdaw-specific stuff and made it more flexible.
cpu/avr/usb/serial: Updates to CDC serial implementation.
Various tweaks to the uip network stack.
platform/econotag: Allow RPL and Router settings to be overridden.
cpu/native: Add file-backed simulated EEPROM to native cpu.

This patch removes a defunct EEPROM implementation from the native
platform and provides a new EEPROM implementation for the native cpu.
The previous implementation appears to be vestigal.

This is useful for testing code which uses the EEPROM without running
the code on the actual hardware.

By default the code will create a new temporary file as the EEPROM
backing, reinitializing each time. If you would like to preserve the
EEPROM contents or specify a specific EEPROM file to use, you can set the
`CONTIKI_EEPROM` environment variable to the name of the EEPROM file you
wish to use instead. If it already exists, its contents will be used.
If it does not already exist, it will be created and initialized by
filling it with `0xFF`---just like a real EEPROM.

A new example is also included, which was used to verify the correctness
of the implementation. It can easily be used to verify the EEPROM
implementations of other targets.
Merge branches 'pull-requests/core-net-bridge-mode', 'pull-requests/core-net-uip-loopback', 'pull-requests/cpu-avr-avrdude-mcu', 'pull-requests/cpu-avr-bootloader', 'pull-requests/cpu-avr-rf230bb-cleanup-hooks', 'pull-requests/cpu-avr-rndis-refactor', 'pull-requests/cpu-avr-usb-cdc-serial-update', 'pull-requests/cpu-native-eeprom', 'uip-updates', 'pull-requests/platform-econotag-uip-rpl-override' and 'pull-requests/settings-for-all-targets' into bleeding-edge
Merge branch 'pull-requests/platform-avr-ravenusb-leds' into bleeding-edge

Conflicts:
	platform/avr-ravenusb/contiki-conf.h