Nightly builds restored

[Andrus Adamchik <an...@objectstyle.org>]

Just updated the nightly build script to Maven. It works and produces  
an assembly. E.g.:

http://objectstyle.org/downloads/cayenne/nightly/2006-9-13/

Assembly is still work in progress. A few things that we still need  
to work on:

* Modeler jar is no longer runnable by itself
* modeler.sh doesn't use the right classpath, and hence can't start  
the Modeler either.
* there is no cayenne.jar with all deps
* cayenne-jpa-agent jar is not included
* javadocs are jared
* wikidocs are not yet included

Andrus