Predictable results when fed non-text data

[jayvdb]

Need tests, and reliable/predictable exceptions, whenever a binary data (not text) is opened. Typically applications try to open a file with a specific encoding (usually utf-8) and let the exception explain that the input file is not acceptable.

In the bom-open model, the encoding shouldnt be specified, so the application can not rely the UnicodeDecodeException saying a specific encoding which should be used, especially if chardet returns a strange fallback encoding like latin1, or an empty result.

We need tests to ensure that the exception raised for non-textual input is predictable and reasonable, and documented.