(THD->IS_BINLOG_APPLIER()

Problem: Changing server internal variable pseudo_slave_mode
inside a transaction is hitting asserts.

Analysis: pseudo_slave_mode is an internal server variable which
is used to detect whether a thread is binlog applier execution
thread or not. In documentation , we say that
"This variable is for internal server use.
SET pseudo_slave_mode= 0,1 are commands that mysqlbinlog adds to
beginning and end of binary log/relay log dumps.
   . Binary logs cannot contain partial transactions
   . if relay log is having partial transaction at the end, then
      we append "Rollback" and then append SET pseudo_slave_mode= 0".
i.e., there is no real use case inside the server for this variable to
be allowed to change inside a transaction.

Fix: Restricting the invalid use case of pseudo_slave_mode.
Users cannot be able to change pseudo_slave_mode inside a transaction.