PIG-3199: Provide a method to retriever name of loader/storer in PigServer

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1525162 13f79535-47bb-0310-9956-ffa450edef68
PIG-3199: Provide a method to retriever name of loader/storer in PigServer

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1525163 13f79535-47bb-0310-9956-ffa450edef68
PIG-3471: Add a base abstract class for ExecutionEngine (cheolsoo)


git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1525165 13f79535-47bb-0310-9956-ffa450edef68