exceptions:

posix_error_with_filename(): New function which calls
PyErr_SetFromErrnoWithFilename()

The following methods have been changed to call
posix_error_with_filename():

    posix_1str()
    posix_strint()
    posix_strintint()
    posix_do_stat()
    posix_mkdir()
    posix_utime()
    posix_readlink()
    posix_open()

INITFUNC(): os.error (nee PosixError) is PyExc_OSError