Attribute parallel access bug

[James Powell]

https://lavag.org/topic/15857-cr-sqlite-library/?do=findComment&comment=133064

[James Powell]

Use a mutex

https://www.sqlite.org/c3ref/mutex_alloc.html

[James Powell]

Idea: “SQL Statement (with Mutex)” child class that creates a mutex, has a “Get Mutex” property, and releases the mutex on Release (and destroys it on Finalize). Use this class in the Attribute stuff.

[James Powell]

Went with a Mutex in the Attribute Connection class itself. 52ec59b15deb77aeec1a883889bb4d2571d9348d