In a future release of avast , could systems development delete associated Jet .tmp files that are “No Longer Needed”?
You should have posted this in the wishlist topic in the avast! 4.x Home/Pro section. 
That’s the responsibility of the Jet drivers themselves.
If they don’t do that, I’d suggest to check if you have the latest version (of them).
In fact, in normal behavior, the files are deleted.
Maybe, crashes, power failures, etc. will left files behind 
Jet drivers: Try to update the Jet drivers (MDAC package) and see if it helps (http://www.microsoft.com/data).
Great, and thank you so much for your guidance.
I am pleased with my avast! 4 Anti Virus software,
and also installed it for my sister in law two weeks ago, and plan on another sister in law next week.
They were very pleased because it Found a virus that their Prior Anti Virus Company did not notice.