Patch replacing "s*" parsing format by "y*" for:
 - utf_7_decode()
 - utf_8_decode()
 - utf_16_decode()
 - utf_16_le_decode()
 - utf_16_be_decode()
 - utf_16_ex_decode()
 - utf_32_decode()
 - utf_32_le_decode()
 - utf_32_be_decode()
 - utf_32_ex_decode()
 - unicode_escape_decode()
 - raw_unicode_escape_decode()
 - latin_1_decode()
 - ascii_decode()
 - charmap_decode()
 - mbcs_decode()

Using run_tests.sh, all tests are ok (with 19 skipped tests). I guess 
that there is not tests for all these functions :-/

Note: codecs documentation was already correct:

.. method:: Codec.decode(input[, errors])
   (...)
   *input* must be a bytes object or one which provides the read-only 
character
   buffer interface -- for example, buffer objects and memory mapped 
files.