make some of the UnsupportedException messages a little more obvious

h2/src/main/org/h2/command/dml/Select.java

@@ -615,16 +615,16 @@ public class Select extends Query {
         if (isForUpdateMvcc) {
             if (isGroupQuery) {
                 throw DbException.getUnsupportedException(
-                        "FOR UPDATE && GROUP");
+                        "MVCC=TRUE && FOR UPDATE && GROUP");
             } else if (distinct) {
                 throw DbException.getUnsupportedException(
-                        "FOR UPDATE && DISTINCT");
+                        "MVCC=TRUE && FOR UPDATE && DISTINCT");
             } else if (isQuickAggregateQuery) {
                 throw DbException.getUnsupportedException(
-                        "FOR UPDATE && AGGREGATE");
+                        "MVCC=TRUE && FOR UPDATE && AGGREGATE");
             } else if (topTableFilter.getJoin() != null) {
                 throw DbException.getUnsupportedException(
-                        "FOR UPDATE && JOIN");
+                        "MVCC=TRUE && FOR UPDATE && JOIN");
             }
         }
         topTableFilter.lock(session, exclusive, exclusive);

h2/src/main/org/h2/value/DataType.java

@@ -1200,7 +1200,7 @@ public class DataType {
                 return o;
             }
         }
-        throw DbException.getUnsupportedException(paramClass.getName());
+        throw DbException.getUnsupportedException("converting to class " + paramClass.getName());
     }
 
 }