In HEAD, AVR_BIN_PREFIX is set twice, to /usr/share/arduino/hardware/tools/avr/bin/avr- and to /usr/share/arduino/hardware/tools

At least on debian sid, the first is where ar is located.

Prior to
bb20696

arscons finds avr-ar.

I'm happy to write a patch, but I'm not sure what bb20696 is meant to do. Is it sufficient to use AVR_HOME_DUDE in calling avrdude, as in #18?