more diagnostics on failure
implement the releaser role to allow a build and other before-release actions to proceed, without a "you need a Releaser" error
warn early on that releases will be prevented
Dist-Zilla-Plugin-BlockRelease-0.002

          - implement Releaser role so as to not force the use of another
            Releaser plugin
          - warn at the start of the build that releases will be prevented