tostring un persistenceunit#unitkey for easier debugging
diff --git a/meecrowave-jpa/src/main/java/org/apache/meecrowave/jpa/internal/JpaExtension.java b/meecrowave-jpa/src/main/java/org/apache/meecrowave/jpa/internal/JpaExtension.java
index 4da2009..bec3054 100644
--- a/meecrowave-jpa/src/main/java/org/apache/meecrowave/jpa/internal/JpaExtension.java
+++ b/meecrowave-jpa/src/main/java/org/apache/meecrowave/jpa/internal/JpaExtension.java
@@ -201,5 +201,13 @@
         public int hashCode() {
             return hash;
         }
+
+        @Override
+        public String toString() {
+            return "UnitKey{" +
+                    "unitName='" + unitName + '\'' +
+                    ", synchronizationType=" + synchronizationType +
+                    '}';
+        }
     }
 }