Added /opt/local/lib as well as /sw/lib

Fink stores libraries in /sw/lib, but Macports stores them in /opt/local/lib. We add both directories to make sure we find something. Note this might fail if a user has both Macports and Fink installed.
Merge pull request #1 from tvwerkhoven/patch-1

Added /opt/local/lib as well as /sw/lib