than max_connections -- which results in user lockout.

The problem was that the variable thread_count that contains
the number of active threads was interpreted as a number of
active connections.

The fix is to introduce a new counter for active connections.


mysql-test/r/connect.result:
  A test case for Bug#33507: Event scheduler creates more threads
  than max_connections -- which results in user lockout.
mysql-test/t/connect.test:
  A test case for Bug#33507: Event scheduler creates more threads
  than max_connections -- which results in user lockout.
sql/mysql_priv.h:
  1. Polishing: login_connection() and end_connection() need not
     to be public.
  
  2. Introduce connection_count -- a variable to contain the number
     of active connections. It is protected by LOCK_connection_count.
sql/mysqld.cc:
  Use connection_count to count active connections.
sql/sql_connect.cc:
  1. Use connection_count to count active connections.
  2. Make login_connection(), end_connection() private for the module
  as they had to be.