Standardize the error messages generated by constraint failures to a format

of "$TYPE constraint failed: $DETAIL".  This involves many changes to the
expected output of test cases.

FossilOrigin-Name: 54b221929744b1bcdbcc2030fef2e510618afd41

test/savepoint.test

@@ -858,7 +858,7 @@ do_test savepoint-12.2 {
         SAVEPOINT sp2;
           INSERT OR ROLLBACK INTO t4 VALUES(1, 'one');
   }
-} {1 {PRIMARY KEY must be unique}}
+} {1 {UNIQUE constraint failed: t4.a}}
 do_test savepoint-12.3 {
   sqlite3_get_autocommit db
 } {1}