WL#5363: Thread Pool Service Interface

In order to allow thread schedulers to be dynamically loaded,
it is necessary to make the following changes to the server:

- Two new service interfaces

- Modifications to InnoDB to inform the thread scheduler of state changes.

- Changes to the VIO subsystem for checking if data is available on a socket.

- Elimination of remains of the old thread pool implementation.

The two new service interfaces introduces are:

my_thread_scheduler
  A service interface to register a thread
  scheduler.

thd_wait
  A service interface to inform thread scheduler
  that the thread is about to start waiting.

In addition, the patch adds code that:

- Add a call to thd_wait for table locks in mysys
  thd_lock.c by introducing a set function that
  can be used to set a callback to be used when
  waiting on a lock and resuming from waiting.

- Calling the mysys set function from the server
  to set the callbacks correctly.

sql/sql_connect.h

@@ -40,4 +40,8 @@ int check_user(THD *thd, enum enum_server_command command,
 	       const char *passwd, uint passwd_len, const char *db,
 	       bool check_count);
 
+bool login_connection(THD *thd);
+void prepare_new_connection_state(THD* thd);
+void end_connection(THD *thd);
+
 #endif /* SQL_CONNECT_INCLUDED */