[sync] MD5 authentication

[Erik Gustavsson]

> I'm not much of a PHP hacker, but I did a quick search through some 
> SyncML PDF's and they seem to indicate to me that the algorithm is not 
> md5_base64("user:pass:nonce"), but md5_base64(md5_base64("user:pass") 
> . ":nonce")).
>
Actually, this seems to differ between the SyncML versions, also I tried 
to implement the nested version in PHP but couldn't get it to match the 
examples in the PDFs either...

/Erik