[gtkmm] mult-thread support

[Todd Fisher <taf2 lehigh edu>]

Hi,
	I recently switched from writting gtk+ apps in C to C++.  In C
I would typically just use straight pthread function calls to create 
multi-threads and this worked fine with gtk.  I would simply make calls
to gdk_threads_enter and gdk_threads_leave around any critical gtk 
calls.  Now that I'm working in C++ with gtkmm i thought i might try
a similar approach however to my dismay this doesn't seem to be working.
I'm getting the following crash error message:

"Xlib: unexpected async reply (sequence 0x2406)!"

The application does not die but from there on does not behave as 
expected.  Basically, I'd just like to create a new thread that does
some work and updates a scale.  The simplist way to do that
i would think is as follows:

1. create main window   Gtk::Window code
2. spawn worker thread	pthread_create( ..., myfunc, my_scal_widget );
--- 3. main thread is idle giving user ablity to cancel busy task
--- 4. worker thread updates scale widget until work is complete
myfunc(...){
...
my_scale_widget->set_value( new_value );
...
}

3 and 4 happen in parrallel of course.