patch to allow for avrdude to erase by not appending -D

Certain devices (such as the gertduino board) will fail verification if you don't first erase.  At present, -D is passed to avrdude, which suprresses this erase.  I have created a small patch to allow passing --auto-erase 1 to tell it to erase.  Otherwise, it will maintain the existing default behavior.  I would have preferred doing a --auto-erase with no argument, but icouldn't think of a clean way to implement that into an ini file while keeping the command line as argument-less.