encapsulate revisions caused by a single transaction in revisionIndex

[GoogleCodeExporter]

By starting a transaction all including querys should be encapsulated in a 
single "transaction-revision". It should be possible to provide key-value meta 
information to the transaction (e.g. user executing query, query-origin, ...) 
which are reflected in a meta-set inside the transaction-revision.

Advantages would be:
- users expect to be able to see what was caused by a tmql update query as a 
single "transaction-revision"
- users would expect the same for rollbacks
- it is important to connect changes made by users to revisions for security 
and usability reason (future versions of mt or rtm could provide basic 
access-control e.g. modifying a topic is only allowed to he who created a topic)

Original issue reported on code.google.com by [email protected] on 14 Sep 2010 at 1:00