SPARK-4297 [BUILD] Build warning fixes omnibus

There are a number of warnings generated in a normal, successful build right now. They're mostly Java unchecked cast warnings, which can be suppressed. But there's a grab bag of other Scala language warnings and so on that can all be easily fixed. The forthcoming PR fixes about 90% of the build warnings I see now.

Author: Sean Owen <sowen@cloudera.com>

Closes #3157 from srowen/SPARK-4297 and squashes the following commits:

8c9e469 [Sean Owen] Suppress unchecked cast warnings, and several other build warning fixes

1 files changed, 2 insertions, 0 deletions

diff --git a/mllib/src/test/java/org/apache/spark/mllib/feature/JavaTfIdfSuite.java b/mllib/src/test/java/org/apache/spark/mllib/feature/JavaTfIdfSuite.java
index 064263e02c..fbc26167ce 100644
--- a/mllib/src/test/java/org/apache/spark/mllib/feature/JavaTfIdfSuite.java
+++ b/mllib/src/test/java/org/apache/spark/mllib/feature/JavaTfIdfSuite.java
@@ -49,6 +49,7 @@ public class JavaTfIdfSuite implements Serializable {
   public void tfIdf() {
     // The tests are to check Java compatibility.
     HashingTF tf = new HashingTF();
+    @SuppressWarnings("unchecked")
     JavaRDD<ArrayList<String>> documents = sc.parallelize(Lists.newArrayList(
       Lists.newArrayList("this is a sentence".split(" ")),
       Lists.newArrayList("this is another sentence".split(" ")),
@@ -68,6 +69,7 @@ public class JavaTfIdfSuite implements Serializable {
   public void tfIdfMinimumDocumentFrequency() {
     // The tests are to check Java compatibility.
     HashingTF tf = new HashingTF();
+    @SuppressWarnings("unchecked")
     JavaRDD<ArrayList<String>> documents = sc.parallelize(Lists.newArrayList(
       Lists.newArrayList("this is a sentence".split(" ")),
       Lists.newArrayList("this is another sentence".split(" ")),