Improve troubleshooting for missing dune.module

If the library is found, but dune.module is not, we really should give
an error because the #ifdefs in the code will not work as intended.

Print the locations where we expect the library to appear to the console
for better tracking.
Improve detection of dune.module

Remove lib/.libs/ and lib64/ as well as lib/ to find the prefix for the
installation root.
Merge pull request #378 from rolk/378_dunemod

Make finding and installing dune.module redux