Bump version to 0.4rc3
peer: Fix how privileges are dropped

Correctly drop privilege. More specifically:

* Use initgroups to set group permissions correctly.
* Improve error logging.
python: Fix vlmc info method to return size
docs: Provide link to Synnefo upgrade notes

Update 0.4 and 0.4rc2 upgrade notes to explicitly state that in case
Archipelago+NFS is integrated with Synnefo, the Synnefo upgrade notes
must be used in order to adjust permissions.