exchange: extract bundle specification components into own attributes An upcoming patch will enable clients to prefer certain bundles over others. The idea is that we define values of attributes from manifests that are desirable. The BUNDLESPEC attribute is a complex value consisting of multiple parts. Clients may wish to only prefer one of these parts. Having to specify every combination of BUNDLESPEC would be annoying. So, we extract the components of BUNDLESPEC into their own attributes so clients can easily filter on a sub-component.