1.15-0.1.rc1 - Update for new upstream tarball for release candidate
    
    ...Pacemaker-1.1.15-rc1, for full details, see included ChangeLog file or
    https://github.com/ClusterLabs/pacemaker/releases/tag/Pacemaker-1.1.15-rc1
    
    - Adapt spec file more akin to upstream version (also to reflect recent
      changes like ability to built explicitly without Publican-based docs)
    
    Note that patch disabling original built-in notification mechanism is
    no longer needed as the same is achieved natively in the sources,
    and there's brand new, more convoluted (and allegedly compatible)
    implementation of the same.