Unmaintained Deadlock Avoidance by Xon 1.0.21

• Remove use of get_lock which is unsupported in galera clustering, and causes errors in Percona XtraDB Cluster.

• Improve reliability of updating forum's last post so it doesn't sometimes include very old threads

• Fix deleting a post in a thread not updating the forum last post
• Fix Out of range value for column 'discussion_count' error

• Tweak SQL to ensure forum last post stats updates as expected.
  • Note; by design the last post may not update all the time, but on average isn't noticeable on a active forum.

• Report Improvement's logging reply-bans to reports compatibility

• Preserve original ordering of closures when pushing functions out of a transaction
• Hoist updating forum counters out of the new post/add reply transaction. Relaxes updates;
  1. removing a thread will not re-populate the last updated post
  2. moving a thread out of an empty forum has a race condition between the thread saving and the forum counters updating
  3. Forum counters are atomically incremented outside of a large transaction, and atomically conditionally updating the last post via SQL instead of read-mutate-update datawriter cycle

• Always defer user alerts inside a known DataWriter transaction to after that transaction.

• Support profile post/profile post comment/threadmarks

• Revert previous attempt at preventing Like deadlocks.
• Allow Likes to retry once in case of a deadlock.
• Tweak how user alerts counter is incremented to reduce chance of a deadlock by touching less data.

• Remove the use of LOCK FOR UPDATE on thread select when deleting. Instead use Post Delete Time Limit add-on to restrict, independent of edit-times, for how old a post can be and still be deleted.