enforce goal should require dependency collection, not resolution

Enforce goal presently has @requiresDependencyResolution("test"), which forces all dependencies to be downloaded for a project at the start of the lifecycle (e.g. if the plugin is bounded to initialize). If a project has really large dependencies that are resolved on an as-needed basis (e.g. by the assembly plugin), inserting the enforcer plugin (e.g. to enforce certain properties being set) causes everything to be downloaded.

The goal should use the new Maven 3.0 requiresDependencyCollection annotation, which should be sufficient for all existing rules (banned dependencies and such). Any investigation of the contents of the dependencies themselves should be an on-demand resolve by the enforcer.