WIP "avoids clobbering" failure in test suite

This commit preserves a random seed which makes a common "avoids clobbering"
failure in test `two_links_correct_test.rb` reproducible.

Therefore, this is expected to fail Travis, and should not be merged in
current form.

After the relevant bug is fixed on this branch, the `TESTOPTS` setting
in `.travis.yml` **must** be removed.