Note that I'm using
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.1.1</version>
<configuration>
<archiveClasses>true</archiveClasses>
</configuration>
</plugin>
which seems to work. A jar is created in the target directory instead
of .class files.
But I don't know if this is actually also send to GAE servers...