ppl - source package should be versioned

[Matthias Klose <doko@cs.tu-berlin.de>]

Assume we do build the default gcc depending on a libppl0, now the
libppl soname is changed to libppl1, a new ppl source is uploaded, and
suddendly libppl0 isn't available anymore. And we still need to
rebuild gcc using gcc. Making the ppl source versioned (pplX), we
still have the old libppl0 in the archive, and can rebuild gcc, then
remove the old pplX source and binary packages only built from the old
source. Please consider this for the next version bump.

  Matthias