dpkg-shlibdeps: Always try the realpath of the lib as fallback to identify the associ...

dpkg-shlibdeps: Always try the realpath of the lib as fallback to identify the associated package

* scripts/dpkg-shlibdeps.pl (find_packages): Make sure to always
  return [''] for a miss in the 'dpkg -S' query.
* scripts/dpkg-shlibdeps.pl: Always try the realpath($lib) as
  fallback to identify the package (even if it's not a symlink)
  because due to broken RPATH we might get library filenames such as
  "/usr/lib/gcc/i486-linux-gnu/4.2.3/../../../../lib/libssl.so.9.8"
  which is not a symlink and which can still be simplified to
  "/usr/lib/libssl.so.9.8" with realpath().