Tk::ErrorDialog collision breaks 'OK' button

(sorry, premature <Enter> key)

I noticed that a second call to Tk::Error while the errordialog is open would brick our application.
This test demonstrates the problem, but I have not yet fixed it.

I'm intending to replace the Tk::ErrorDialog with something local, sorry.  I think we need a multi-error window...  because we have lots of errors(!).