Issue 380: ALTER TABLE ADD FOREIGN KEY with an explicit index didn't verify the…

Issue 380: ALTER TABLE ADD FOREIGN KEY with an explicit index didn't verify the index can be used, which would lead to a NullPointerException later on.

h2/src/test/org/h2/test/test-1.3.txt

@@ -10,10 +10,10 @@ references test (id) index idx_test_pid;
 > ok
 
 insert into test values (2, null);
-> ok
+> update count: 1
 
 update test set pid = 1 where id = 2;
-> ok
+> exception
 
 drop table test;
 > ok