HIVE-6955 ExprNodeColDesc isSame doesn't account for tabAlias: this affects trait Propagation in Joins (Harish Butani via Gunther Hagleitner)

git-svn-id: https://svn.apache.org/repos/asf/hive/trunk@1590716 13f79535-47bb-0310-9956-ffa450edef68