Added another default reason

src/main/java/envoy/event/HandshakeRejectionEvent.java

@@ -32,6 +32,13 @@ public class HandshakeRejectionEvent implements Event<String> {
 	 */
 	public static final String USER_DOES_NOT_EXIST = "user does not exist";
 
+	/**
+	 * Select this value if a given {@link LoginCredentials} with
+	 * {@link LoginCredentials#isRegistration()}==true points at an already existing
+	 * user
+	 */
+	public static final String USER_EXISTS_ALREADY = "user can not be created as he already exists";
+
 	/**
 	 * Select this value if an unknown error occurred
 	 */