[Dune] PACKAGE_URL

[Christoph Grüninger]

No Markus,
to me you are not blind. I didn't find a definition inside of
dune-common or duneweb neither.

I think it would be nice to use it in dune-common.pc.in to
replace the line
  URL: http://dune-project.org/
by
  URL: @PACKAGE_URL@

Cheers,
Christoph