Add support for non-native rom files in romlist

mupen64plus supports roms in native (*.z64), byteswapped (*.v64) and wordswapped (*.n64) rom files. Unfortunately, m64py only supported native rom files because it didn't swap the also swapped big endian crc values back to the unswapped host ordered crc values for non-native rom files. This caused crc checks to fail for these rom files.

This fixes bug #12