Moved classes from messaging package to sync package.

briar-api/src/org/briarproject/api/sync/MessageId.java

@@ -0,0 +1,23 @@
+package org.briarproject.api.sync;
+
+import org.briarproject.api.UniqueId;
+
+import java.util.Arrays;
+
+/**
+ * Type-safe wrapper for a byte array that uniquely identifies a
+ * {@link Message}.
+ */
+public class MessageId extends UniqueId {
+
+	public MessageId(byte[] id) {
+		super(id);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (o instanceof MessageId)
+			return Arrays.equals(id, ((MessageId) o).id);
+		return false;
+	}
+}