HIVE-3987

Summary: ON keyword is required and is first one needed at beginning of ptf func defintion. Adds named parameter support as well. Note that this just updates the grammar for named params. They are still treated positionally internally. This makes sql syntax compliant but needs more work to loosen the restriction of argument needing to be positional.

Test Plan: Existing test cases are updated.

Reviewers: hbutani

Differential Revision: https://reviews.facebook.net/D9027

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/ptf-windowing@1451930 13f79535-47bb-0310-9956-ffa450edef68