Here is another patch, this time for the fallback-md5-module. I know
that situations are rare where openssl is not present but threading is.
However they might occur out there and the md5module needed some love
anyway:

- The MD5 class from the fallback module can now also use threads with
'small locks'
- The behaviour regarding unicode data input is now consistent as to
what the openssl-driven classes do.
- Some code cleanup.


I might act on the sha modules as way the next days. sha256.c still
accepts 's#'...


Also see issue #4751