PIG-2433: Jython import module not working if module path is in classpath

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1430649 13f79535-47bb-0310-9956-ffa450edef68
PIG-3115: Distinct Build-in Function Doesn't Handle Null Bags

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1430689 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' of https://github.com/apache/pig into trunk