Add test-case for Bug #2438181 (which passes in Tcl 8.4 but fails in 8.5/8.6).
Provided by Poor Yorick
Fix bug #2438181: Incorrect error reporting in traces. 
Test-case and fix provided by Poor Yorick.
revert mangling with "code" variable. This caused unrelated var.test failures.
Fix bug #2438181: Incorrect error reporting in traces. 
Test-case and fix provided by Poor Yorick.