#2813 - Sometimes subquery use wrong alias in SQL

The reason for this is that as part of DefaultOrmQuery.copy() it uses
DefaultExpressionList.copy() and that assumed that expressions were
safe to share which is NOT the case for IN and EXISTS sub-query expressions
so InQueryExpression and ExistsQueryExpression

The effective fix for this is that DefaultExpressionList.copy() changes
to call SpiExpression.copy() and for InQueryExpression and ExistsQueryExpression
to implement that copy() by creating a copy of the sub-query.

A "side-fix" is that in DefaultOrmQuery.createExtraJoinsToSupportManyWhereClause()
it was creating an instance of ManyWhereJoins, then mutating it ... and if we
change that to only doing the assignment at the end (object assignment is atomic)
then racy access reading ManyWhereJoins would always get a fully completed non-mutating
instance of ManyWhereJoins. Noting this because it kind of points to where I think
the race condition is (in createExtraJoinsToSupportManyWhereClause()) but noting that
with the change to DefaultExpressionList.copy() this "side-fix" isn't required per say.

ebean-test/src/test/java/org/tests/query/TestQueryFindPagedList.java

@@ -70,11 +70,12 @@ public class TestQueryFindPagedList extends BaseTestCase {
       .setMaxRows(3)
       .findPagedList();
 
-    Future<Integer> rowCount = pagedList.getFutureCount();
+    pagedList.loadCount();
     List<Order> orders = pagedList.getList();
 
     // these are each getting the total row count
     int totalRowCount = pagedList.getTotalCount();
+    Future<Integer> rowCount = pagedList.getFutureCount();
     Integer totalRowCountWithTimeout = rowCount.get(30, TimeUnit.SECONDS);
     Integer totalRowCountViaFuture = rowCount.get();