Code review comment for lp:~vlad-lesin/percona-server/sql_timeout

Everything is done except making SQL_TIMEOUT not only session but global variable too. Because blueprint describes it as a session variable. It's not an issue to do this but in this case we should change the blueprint too.

Each item in the queue has a pointer to the thread object to have
ability to invoke "kill query" function for that thread. Every time we use sql_timeout we push that pointer and expiration time to the queue. And after the query is executed we remove the item from the queue. The "remove" operation searches the queue item with certain thread pointer using hash table.