Set BREE to at least JavaSE-1.6 when building OSGi bundles.
    
    Since Fedora 17, we need an Execution Environment of at least JavaSE-1.6
    for Eclipse bundles. Eclipse Juno platform bundles depend on
    javax.annotation. In Fedora this is provided by geronimo-annotation, but
    has a dependency on javax.lang.model (since 1.6).