Allow subclasses of UnitOfWork (remove 'final').

pom.xml

@@ -5,7 +5,7 @@
     <modelVersion>4.0.0</modelVersion>
     <groupId>net.helenus</groupId>
     <artifactId>helenus-core</artifactId>
-    <version>2.0.29-SNAPSHOT</version>
+    <version>2.0.30-SNAPSHOT</version>
     <packaging>jar</packaging>
 
     <name>helenus</name>

src/main/java/net/helenus/core/UnitOfWork.java

@@ -8,7 +8,7 @@ import java.util.*;
 
 
 /** Encapsulates the concept of a "transaction" as a unit-of-work. */
-public final class UnitOfWork implements AutoCloseable {
+public class UnitOfWork implements AutoCloseable {
   private final List<UnitOfWork> nested = new ArrayList<>();
   private final HelenusSession session;
   private final UnitOfWork parent;