Release 1.3.3 is for OS X users who need to explicitly set JAVA_HOME. Any other OS users can simply ignore the release.
Since 1.3.0, Rjb uses Java Framework JVM on OS X but it also see JAVA_HOME environment variable. This behavior is not so good because JAVA_HOME does not contain JVM usually on OS X. So 1.3.3 Rjb check JAVA_HOME and if there is JVM or not, and rearrange JVM location if it's not there.
Warning: I push 2 types of gems into RubyGems.org. One is platform independent and one is darwin-universal. But darwin-universal gem is for originally bundled Ruby-1.8.7, so another ruby binary users may meet the trouble if install it. Please install platform independent gem using 'gem install --platform ruby rjb -v 1.3.3'.