Oh right yeah forgot that. You have to now specify the upload tool in the boards.txt file.
To do that you need to add these lines for each entry:
attiny84at1.bootloader.tool=avrdude
attiny84at1.upload.tool=avrdude
Also, if you haven't already got one, you may have to copy the programmers.txt file from the arduino folder as well. I am not sure that this is needed though as it results in duplicate programmers in the IDE programmer window.