Fixed atmega bootloader

Well, I didn't particularly want to learn about the intricate details of getting Atmega bootloaders up and running, but it appears it's working.

I was a bit nervous when I did the chip erase as that was a definite farewell to the stock AVR loader, but there didn't seem to be any other options. After a couple of hours with no bootloader at all, my Z80 bit-bashing code finally prevailed:

Now, I can get on to the task I actually wanted to do... write a JTAG programmer for the PROM!