[FLINK-2638] [core] Add @SafeVarargs to the ExecutionEnvironment's "fromElements(...)" method.

This closes #1109

flink-java/src/main/java/org/apache/flink/api/java/ExecutionEnvironment.java

@@ -703,7 +703,8 @@ public abstract class ExecutionEnvironment {
 	 * @param data The elements to make up the data set.
 	 * @return A DataSet representing the given list of elements.
 	 */
-	public <X> DataSource<X> fromElements(X... data) {
+	@SafeVarargs
+	public final <X> DataSource<X> fromElements(X... data) {
 		if (data == null) {
 			throw new IllegalArgumentException("The data must not be null.");
 		}

flink-staging/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/environment/StreamExecutionEnvironment.java

@@ -553,7 +553,8 @@ public abstract class StreamExecutionEnvironment {
 	 * 		The type of the returned data stream
 	 * @return The data stream representing the given array of elements
 	 */
-	public <OUT> DataStreamSource<OUT> fromElements(OUT... data) {
+	@SafeVarargs
+	public final <OUT> DataStreamSource<OUT> fromElements(OUT... data) {
 		if (data.length == 0) {
 			throw new IllegalArgumentException("fromElements needs at least one element as argument");
 		}