Tcl/tk 8.6, itcl/itk 4.0.0, etc.

I'm currently trying to make insight run properly on Fedora rawhide
(future release 21). This features tcl/tk 8.6 and itcl/itk 4.0.0.
Currently, itcl/itk/iwidgets still have bugs but I fixed them locally
(at least those bugs preventing these packages to start).

I still work on the base of a (heavily patched) insight snapshot of
2012/04/03, mainly because porting gdb patches to insight is a big work
and not easy those days when gdb has moved to git while insight has not.

Anyway: when I try to run insight on F21, I get an error:

invalid command name "::.srcwin0.srcwin"
invalid command name "::.srcwin0.srcwin"
    while executing
"::.srcwin0.srcwin sizeWinByChild toolbar"
    ("after" script)

I located this statement in file srcwin.itb, line 43 as:

after idle "
      update idletasks
      $this sizeWinByChild toolbar"

This file has'nt changed for 5 years...

I have not enough (i)tcl/tk to understand + fix this problem: does
anybody has some clue about it ?

If someone runs a rawhide environment, you can find my latest (failing)
package for it at
http://koji.fedoraproject.org/koji/taskinfo?taskID=3D7032279, but you
won't reach (for now) the problem until itcl/itk/iwidgets get patched...

Thanks in advance.
Regards,
Patrick