HIVE-4140

Summary: Specifying alias for windowing function. Also moved windowing rules from FromClauseParser.g to SelectClauseParser.g

Test Plan: Updated existing tests.

Reviewers: hbutani

Differential Revision: https://reviews.facebook.net/D9249

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/ptf-windowing@1454661 13f79535-47bb-0310-9956-ffa450edef68