I believe the problem is not that you need BSF -- because you are using java6 (you have to to compile Solr) so BSF isn't needed. The problem (i think) is that FreeBSD's JDK doesn't include javascript by default - i believe you just need to install the rhino "js.jar"....
You are right. FreeBSD OpenJDK do not include Javascript.
I finally got it work, commented at https://issues.apache.org/jira/browse/LUCENE-4415
