clarify collection behavior with pipelined connection

REDIS-100

src/main/java/org/springframework/data/redis/support/collections/AbstractRedisCollection.java

@@ -26,6 +26,9 @@ import org.springframework.data.redis.core.RedisOperations;
  * Base implementation for {@link RedisCollection}.
  * Provides a skeletal implementation.
  * 
+ * Note that the collection support works only with normal, non-pipeline/multi-exec connections as it requires
+ * a reply to be sent right away. 
+ * 
  * @author Costin Leau
  */
 public abstract class AbstractRedisCollection<E> extends AbstractCollection<E> implements RedisCollection<E> {
@@ -84,11 +87,6 @@ public abstract class AbstractRedisCollection<E> extends AbstractCollection<E> i
 		return modified;
 	}
 
-	public boolean retainAll(Collection<?> c) {
-		throw new UnsupportedOperationException();
-	}
-
-	
 	public boolean equals(Object o) {
 		if (o == this)
 			return true;

src/main/java/org/springframework/data/redis/support/collections/DefaultRedisSet.java

@@ -28,6 +28,9 @@ import org.springframework.data.redis.core.RedisOperations;
 /**
  * Default implementation for {@link RedisSet}.
  * 
+ * Note that the collection support works only with normal, non-pipeline/multi-exec connections as it requires
+ * a reply to be sent right away.
+ *  
  * @author Costin Leau
  */
 public class DefaultRedisSet<E> extends AbstractRedisCollection<E> implements RedisSet<E> {

src/main/java/org/springframework/data/redis/support/collections/DefaultRedisZSet.java

@@ -28,6 +28,9 @@ import org.springframework.data.redis.core.ZSetOperations.TypedTuple;
 /**
  * Default implementation for {@link RedisZSet}.
  * 
+ * Note that the collection support works only with normal, non-pipeline/multi-exec connections as it requires
+ * a reply to be sent right away. 
+ *
  * @author Costin Leau
  */
 public class DefaultRedisZSet<E> extends AbstractRedisCollection<E> implements RedisZSet<E> {