[SPARK-17035] [SQL] [PYSPARK] Improve Timestamp not to lose precision for all cases

## What changes were proposed in this pull request?

`PySpark` loses `microsecond` precision for some corner cases during converting `Timestamp` into `Long`. For example, for the following `datetime.max` value should be converted a value whose last 6 digits are '999999'. This PR improves the logic not to lose precision for all cases.

**Corner case**
```python
>>> datetime.datetime.max
datetime.datetime(9999, 12, 31, 23, 59, 59, 999999)
```

**Before**
```python
>>> from datetime import datetime
>>> from pyspark.sql import Row
>>> from pyspark.sql.types import StructType, StructField, TimestampType
>>> schema = StructType([StructField("dt", TimestampType(), False)])
>>> [schema.toInternal(row) for row in [{"dt": datetime.max}]]
[(253402329600000000,)]
```

**After**
```python
>>> [schema.toInternal(row) for row in [{"dt": datetime.max}]]
[(253402329599999999,)]
```

## How was this patch tested?

Pass the Jenkins test with a new test case.

Author: Dongjoon Hyun <[email protected]>

Closes apache#14631 from dongjoon-hyun/SPARK-17035.

Author: dongjoon-hyun

python/pyspark/sql/tests.py

@@ -178,6 +178,11 @@ def test_datetype_equal_zero(self):
         dt = DateType()
         self.assertEqual(dt.fromInternal(0), datetime.date(1970, 1, 1))
 
+    # regression test for SPARK-17035
+    def test_timestamp_microsecond(self):
+        tst = TimestampType()
+        self.assertEqual(tst.toInternal(datetime.datetime.max) % 1000000, 999999)
+
     def test_empty_row(self):
         row = Row()
         self.assertEqual(len(row), 0)

python/pyspark/sql/types.py

@@ -189,7 +189,7 @@ def toInternal(self, dt):
         if dt is not None:
             seconds = (calendar.timegm(dt.utctimetuple()) if dt.tzinfo
                        else time.mktime(dt.timetuple()))
-            return int(seconds * 1e6 + dt.microsecond)
+            return int(seconds) * 1000000 + dt.microsecond
 
     def fromInternal(self, ts):
         if ts is not None: