My tests with 7-zip and WinRAR conviced me that it's not a good idea to use utf-8 *by default* on Windows. But since mbcs doesn't support surrogateescape error handler, we should restore the previous behaviour just for this encoding.

tarfile_mbcs_errors.patch creates a function choose_errors() which determine the best error handler depending on the encoding and the mode (read or write):
 - "strict" to write with mbcs
 - "replace" to read with mbcs
 - "surrogateescape" otherwise

Please, review my changes on the documentation :-)

On Windows, patched tarfile works exactly as Python 3.1.