(PUP-2683) Fix fact terminus to load facts without '.' on the load path.

The fix to PUP-2478 removed '.' from the load path, which only affected
Ruby 1.8.7. However, the fact terminus does "load <filename>" to load
module facts. In Ruby 1.8.7, this will fail to load because '.' is no
longer on the load path. In Ruby 1.9.3+, loading with just a filename
assumes the current directory even without '.' on the load path.

This commit fixes the issue by joining '.' with the filename which
works in all currently supported Ruby versions.