Merge pull request apache#35 in BDP/apache-spark from date-udf to netflix/2.1.1-unstable

* commit '8dbe1a82a138ddb6d2f13c799225bfa13c8875ab':
  NETFLIX-BUILD: 1. Use session chronology and zone instead of UTC 2. Add spark.sql.enableNetflixUdfStrictEval config to return nulls or throw errors during UDF evaluation 3. Accept both epoch and epochms as inputs to UDFs 4. Add unit tests for other date udfs

Author: Vinitha Reddy Gankidi