This patch fixes the bug#13737343 (formerly known as 64374): XA TRANSACTIONS

AND SAVEPOINT.
      
The bug was introduced by the patch for bug#11766752. This patch sets too
strong condition on XA state for SAVEPOINT statement that disallows its
execution during XA transaction. But since the statement SAVEPOINT doesn't
imply implicit commit we can allow its handling during XA transaction.

The patch explicitly check for transaction state against states XA_NOTR
and XA_ACTIVE for which the handling of statement SAVEPOINT for XA
transaction is allowed.

mysql-test/t/xa.test:
  Testcase was adjusted for bug#13737343. Now SAVEPOINT is allowed for XA
  transactions in ACTIVE state.

mysql-test/r/xa.result

@@ -174,7 +174,6 @@ CREATE TABLE t1 (a INT) engine=InnoDB;
 XA START 'a';
 INSERT INTO t1 VALUES (1);
 SAVEPOINT savep;
-ERROR XAE07: XAER_RMFAIL: The command cannot be executed when global transaction is in the  ACTIVE state
 XA END 'a';
 SELECT * FROM t1;
 ERROR XAE07: XAER_RMFAIL: The command cannot be executed when global transaction is in the  IDLE state

mysql-test/t/xa.test

@@ -298,7 +298,6 @@ CREATE TABLE t1 (a INT) engine=InnoDB;
 XA START 'a';
 INSERT INTO t1 VALUES (1);
 
---error ER_XAER_RMFAIL
 SAVEPOINT savep;
 
 XA END 'a';

sql/transaction.cc

@@ -390,7 +390,7 @@ bool trans_savepoint(THD *thd, LEX_STRING name)
     DBUG_RETURN(FALSE);
 
   enum xa_states xa_state= thd->transaction.xid_state.xa_state;
-  if (xa_state != XA_NOTR)
+  if (xa_state != XA_NOTR && xa_state != XA_ACTIVE)
   {
     my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
     DBUG_RETURN(TRUE);