Updated bitfile for Papilio One 500

Due to a miscalculation, the Alpha 4 image for Papilio One 500 would overwrite the FPGA bitfile when you uploaded a sketch, which in turn would cause it to require a new bitfile upload when power cycled. This is now fixed, and I published a new bitfile for it:

http://www.alvie.com/zpuino/download.html

Thanks a lot to the reporter and tester, "dack", who I spoke with on IRC on #gadgetfactory channel (FreeNode).

Alvie