pom.xml: Add rt.jar as a compile dependency for mvn test.

Needed for package sun.org.mozilla.javascript.internal in JsTest.
SnowServlet: User logger.info instead of System.out.println

Use SLF4J's output variables instead of +
Pass raw exception object to SLF4J
Merge pull request #31 from evanj/master

Minor changed: Fix "mvn test" and replace System.out.println with logger.info