Fix scaladoc faux-error.

Visibility rules for static members are different in Scala and Java, and this case requires an explicit static import. Even though these are Java files, they are run through scaladoc, which enforces Scala rules.

Fix SPARK-7726

Author: dragos

network/shuffle/src/main/java/org/apache/spark/network/shuffle/protocol/OpenBlocks.java

@@ -24,6 +24,9 @@
 
 import org.apache.spark.network.protocol.Encoders;
 
+// Needed by ScalaDoc. See SPARK-7726
+import static org.apache.spark.network.shuffle.protocol.BlockTransferMessage.Type;
+
 /** Request to read a set of blocks. Returns {@link StreamHandle}. */
 public class OpenBlocks extends BlockTransferMessage {
   public final String appId;

network/shuffle/src/main/java/org/apache/spark/network/shuffle/protocol/RegisterExecutor.java

@@ -22,6 +22,9 @@
 
 import org.apache.spark.network.protocol.Encoders;
 
+// Needed by ScalaDoc. See SPARK-7726
+import static org.apache.spark.network.shuffle.protocol.BlockTransferMessage.Type;
+
 /**
  * Initial registration message between an executor and its local shuffle server.
  * Returns nothing (empty bye array).

network/shuffle/src/main/java/org/apache/spark/network/shuffle/protocol/StreamHandle.java

@@ -20,6 +20,9 @@
 import com.google.common.base.Objects;
 import io.netty.buffer.ByteBuf;
 
+// Needed by ScalaDoc. See SPARK-7726
+import static org.apache.spark.network.shuffle.protocol.BlockTransferMessage.Type;
+
 /**
  * Identifier for a fixed number of chunks to read from a stream created by an "open blocks"
  * message. This is used by {@link org.apache.spark.network.shuffle.OneForOneBlockFetcher}.

network/shuffle/src/main/java/org/apache/spark/network/shuffle/protocol/UploadBlock.java

@@ -24,6 +24,9 @@
 
 import org.apache.spark.network.protocol.Encoders;
 
+// Needed by ScalaDoc. See SPARK-7726
+import static org.apache.spark.network.shuffle.protocol.BlockTransferMessage.Type;
+
 
 /** Request to upload a block with a certain StorageLevel. Returns nothing (empty byte array). */
 public class UploadBlock extends BlockTransferMessage {