gdb output:
Program received signal SIGFPE, Arithmetic exception.
0x0804c78d in pngwriter::drawbottom_blend (this=0xbf89fbdc, x1=9, y1=39,
x2=85, x3=93, y3=39, opacity=0.72510022277715624, red=7242, green=18984,
blue=24996) at pngwriter.cc:4536
4536 long cl=((x3-x1)*256)/(y3-y1);
(note that y1 == y3)
2009-03-03 21:34:30 UTC in PNGwriter