proper CODE ref refcounting in Tcl::call (well, almost)

Hi,

Some time ago (long ago) we tried to establish a way when CODE REFs
created in Tcl::call would be properly refcounted, but then gave up.

it appears that now I found a way how it could be done in a 99.999%
clean way.

I've just commited into repo Tcl.pm on github, 
https://github.com/gisle/tcl.pm/commit/fe4305492ee9fc845c992fae13c91fa01da26cdb
so following piece of code behaves correctly:


use strict;
use Tcl;
use Tcl::Tk;

my $int = new Tcl::Tk;

$int->Eval(<<'EOS');
package require Tk
pack [button .b1 -text b1]
pack [button .b2 -text b2]
pack [button .b3 -text b3]
focus .b1
EOS

if (1) {
    my $r = 'aaa';
$int->call('.b1','configure',-command=>sub {print ".b1\n";});
$int->call('.b2','configure',-command=>sub {print ".b2\n";});
$int->call('.b3','configure',-command=>sub {
	print "reconfiguring .b2 r=$r\n";
	$r++;
	$int->call('.b2','configure',-command=>sub {print "***.B2*** $r;\n";},
-text=> '.B2');
    });
}

$int->icall('tkwait', 'window', '.');


Button .b3 on click changes -command for .b2 button, and this command
resolves to new TCL name each time, because of some scope lexical. 

However previous -command for .b2 button is now destroyed, due to my
latest change (well, not destroyed very initial -command for .b2, for
some known reasons)

I will also add t/ test file for this,
also I'll remove debugging output, and also fix some spur at the end - 

====
called Tcl_FindHashEntry on deleted table
Aborted
====

I would like to hear from experts - does it works for all.

Also, is it useful to do same work for Tcl variables as well, or tcl
vars are not that often?

Thanks,
Vadim.