Semantic fix unavailable improvements
If an IMPROVEMENT production target moves up from the worklist to current production, and is unavailable, we get the message
"......which is no longer available."
This is true for cases where it postpones and should say "is not yet available" because you didn't get the tech.
Changing the language to "which is currently unavailable" fixes this semantics for all cases of 1) no longer available and 2) not yet available.