fix Issue 9266 - Cannot define two Tuple objects.

If the semantics in template instance is already done (`inst != NULL`), `syntaxCopy` should copy members from original template declaration (== `tempdecl`).
Merge pull request #1447 from 9rnsr/fix9266

Issue 9266 - Cannot define two Tuple objects. (Regression in 2.061)
Fixes Issue 8948 - Make error message more readable when assigning func/dg expression to a func/dg type