Fix ColumnModel.getAllLeafColumns so 3-level primary keys work

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/src/com/google/gwtorm/schema/ColumnModel.java b/src/com/google/gwtorm/schema/ColumnModel.java
index 6a56949..23e166b 100644
--- a/src/com/google/gwtorm/schema/ColumnModel.java
+++ b/src/com/google/gwtorm/schema/ColumnModel.java
@@ -90,7 +90,7 @@
     final ArrayList<ColumnModel> r = new ArrayList<ColumnModel>();
     for (final ColumnModel c : nestedColumns) {
       if (c.isNested()) {
-        r.addAll(c.getNestedColumns());
+        r.addAll(c.getAllLeafColumns());
       } else {
         r.add(c);
       }