I've wrote test for my feature. You can see all in the patch. Also,
I've added this in ChangeLog.

I don't know TCL but I hope that my test script is written correctly
(at least in the main).

If necessary, I can write new version with 'set backtrace nopath'
instead of 'backtrace nopath'.

Is this version ok? If Yes, I will send filled form of copyright
assignment to fsf-records(d0t)gnu.org and Tom Tromey.