Faster database update to 3.3 on PostgreSQL & MySQL

We now use one single update statement instead of using a loop and
iterating over all articles with a message_id.

Unfortunately, Oracle has no native MD5 function.
I could not get SQL Servers' MD5 function to produce output similar
to what MainObject outputs.

Possible improvements:

 - create a function in Oracle. Ref:
    http://www.pilcrow.nl/2010/12/md5-function-in-oracle

 - check how to make SQL Servers' HASHBYTES return a *correct* md5:
    http://technet.microsoft.com/en-us/library/ms174415.aspx