innodb_lock_waits. See
https://svn.innodb.com/innobase/InformationSchema/TransactionsAndLocks
for design notes.
Things that need to be resolved before this goes live:
* MySQL must add thd_get_thread_id() function to their code
http://bugs.mysql.com/30930
* Allocate memory from mem_heap instead of using mem_alloc()
* Copy table name and index name into the cache because they may be
freed later which will result in referencing freed memory
Approved by: Marko
