[SPARK-19561][SQL] add int case handling for TimestampType

## What changes were proposed in this pull request?

Add handling of input of type `Int` for dataType `TimestampType` to `EvaluatePython.scala`. Py4J serializes ints smaller than MIN_INT or larger than MAX_INT to Long, which are handled correctly already, but values between MIN_INT and MAX_INT are serialized to Int.

These range limits correspond to roughly half an hour on either side of the epoch. As a result, PySpark doesn't allow TimestampType values to be created in this range.

Alternatives attempted: patching the `TimestampType.toInternal` function to cast return values to `long`, so Py4J would always serialize them to Scala Long. Python3 does not have a `long` type, so this approach failed on Python3.

## How was this patch tested?

Added a new PySpark-side test that fails without the change.

The contribution is my original work and I license the work to the project under the project’s open source license.

Resubmission of https://github.com/apache/spark/pull/16896. The original PR didn't go through Jenkins and broke the build. davies dongjoon-hyun

cloud-fan Could you kick off a Jenkins run for me? It passed everything for me locally, but it's possible something has changed in the last few weeks.

Author: Jason White <jason.white@shopify.com>

Closes #17200 from JasonMWhite/SPARK-19561.

python/pyspark/sql/tests.py

@@ -1555,6 +1555,14 @@ class SQLTests(ReusedPySparkTestCase):
         self.assertEqual(now, now1)
         self.assertEqual(now, utcnow1)
 
+    # regression test for SPARK-19561
+    def test_datetime_at_epoch(self):
+        epoch = datetime.datetime.fromtimestamp(0)
+        df = self.spark.createDataFrame([Row(date=epoch)])
+        first = df.select('date', lit(epoch).alias('lit_date')).first()
+        self.assertEqual(first['date'], epoch)
+        self.assertEqual(first['lit_date'], epoch)
+
     def test_decimal(self):
         from decimal import Decimal
         schema = StructType([StructField("decimal", DecimalType(10, 5))])

sql/core/src/main/scala/org/apache/spark/sql/execution/python/EvaluatePython.scala

@@ -112,6 +112,8 @@ object EvaluatePython {
     case (c: Int, DateType) => c
 
     case (c: Long, TimestampType) => c
+    // Py4J serializes values between MIN_INT and MAX_INT as Ints, not Longs
+    case (c: Int, TimestampType) => c.toLong
 
     case (c, StringType) => UTF8String.fromString(c.toString)