custom manifest and war overlays

Despite the fact that it is possible to generate a custom manifest as described in war-manifest-guide, it's not good enough when using the overlays mechanism. The maven-war-plugin can't take into account an existing manifest. It can just generate a new one with the corresponding configuration in the pom.

However, if you use the overlays mechanism, you rather want to keep the manifest from your common war (see custom-manifest-war-overlays.zip in attachment).