cooja: Allow CFLAGS to filter thru
core/net/resolv: Avoid using `snprintf()`.
Add to native-target-osx branch.
cpu/avr/dev/clock: Working `clock_sleep_with_max_duration()` implementation.
cpu/avr/bootloader: Fixed `bootloader_is_present()` function.
cpu/avr/dev/usb: Various minor updates.
Misc AVR updates.