Synchronize ALTER TABLE EXCHANGE PARTITION and PURGE grammar in sql_yacc.yy and sql_yacc_ora.yy

  bool stmt_alter_table_exchange_partition(Table_ident *table);

  void stmt_purge_to(const LEX_CSTRING &to);

  bool stmt_purge_before(Item *item);

alter_commands:

          ...

        | EXCHANGE_SYM PARTITION_SYM alt_part_name_item

          WITH TABLE_SYM table_ident have_partitioning

          {

            if (Lex->stmt_alter_table_exchange_partition($6))

              MYSQL_YYABORT;

          }

        ;

purge:

          PURGE master_or_binary LOGS_SYM TO_SYM TEXT_STRING_sys

          {

            Lex->stmt_purge_to($5);

          }

        | PURGE master_or_binary LOGS_SYM BEFORE_SYM expr_no_subselect

          {

            if (Lex->stmt_purge_before($5))

              MYSQL_YYABORT;

          }

        ;