[avr-gcc-list] Small bug in avrtest

[Wouter van Gulik]

Hi list/Paulo,

I just wanted to let you know before someone else also spends an evening 
searching this bug :D

The file is opened with the "rt" option. I don't know what it's supposed 
to do, but it makes my Mingw Windows compiled version open files only 
half or so. Leading to illegal "pc out of bounds" errors.

I changed it to "rb" and all was good.

HTH,

Wouter