* Overhaul the way kernel modules are built.

  * Overhaul the way kernel modules are built.
    - Recommend linux-image rather than kernel-image for newer kernels.
    - Always recommend the kernel package; since it's only a recommends,
      there's no need to special-case the hand-built kernel case.
    - Be less fragile about how the kernel version is used in prep-modules
      to support other ways kernel modules are built.  (Closes: #341836)
    - Add Build-Depends and Uploaders to the openafs-modules-source
      control file.
    - Remove unused parts of prep-modules and heavily comment it.