Add a commit to explain the modify

Add a commit to tell the user why we had a judgement here.
And use `until` instead of `to` for the purpose of avoid the limit size of the input seq and make the code more readable.

Author: SaintBacchus

examples/src/main/scala/org/apache/spark/examples/SparkPi.scala

@@ -27,8 +27,8 @@ object SparkPi {
     val conf = new SparkConf().setAppName("Spark Pi")
     val spark = new SparkContext(conf)
     val slices = if (args.length > 0) args(0).toInt else 2
-    val n = math.min(100000L * slices, Int.MaxValue -1).toInt
-    val count = spark.parallelize(1 to n, slices).map { i =>
+    val n = math.min(100000L * slices, Int.MaxValue).toInt // avoid overflow
+    val count = spark.parallelize(1 until n, slices).map { i =>
       val x = random * 2 - 1
       val y = random * 2 - 1
       if (x*x + y*y < 1) 1 else 0