utf_8_java.patch: Implement "utf-8-java" encoding.
 * It has no alias
 * 'a\0b'.encode('utf-8-java') returns b'a\xc0\x80b'
 * b'a\xc0\x80b'.decode('utf-8-java') returns 'a\x00b'
 * I added some tests to utf-8 codec (test_invalid, test_null_byte)
 * I added many tests for utf-8-java codec
 * I choosed to copy utf8_code_length as utf8java_code_length instead of adding some if to not slow down UTF-8 codec
 * Decoder: 2 byte sequences may be *a little bit* slower for UTF-8:
"if ((s[1] & 0xc0) != 0x80)"
   is replaced by 
"if ((ch <= 0x007F && (ch != 0x0000 || !java)) || ch > 0x07FF)"
 * Encoder: encode chars in U+0000-U+007F may be *a little bit* slower for UTF-8: I added (ch == 0x00 && java) test

For the doc, I just added a line "utf-8-java" in the codec list, but I did not add a paragraph to explain how this codec is different to utf-8. Does anyone have a suggestion?