files with invalid utf-8 characters cause a crash

[pierstitus]

UnicodeDecodeError is raised:

UnicodeDecodeError: 'utf-8' codec can't decode byte 0x92 in position 2717: invalid start byte

options would be to use errors='backslashreplace' in the open() calls in klonpatiencediff.py, or else doing the whole diff algorithm in binary and leaving the errors in. errors='surrogateescape' doesn't work because the surrogates are not allowed by python to be converted back.