guile-gtk 1.2 threads protection

[Kevin Ryde]

I've realized that the bits I put in the guile-gtk-1.2 manual about
the interface using a mutex to protect an application from two threads
calling Gtk aren't right.

It was probably close enough in 1.6, with the threading there only
switching within a guile func.  But in 1.8 the SCM_DEFER_INTS that I
had in mind certainly doesn't do the right thing.

One possibility would be to have guile-gtk functions put
gtk_threads_enter and gtk_threads_leave around each gtk/gdk call.
It'd probably want a recursive mutex since it might be nested within
application uses of gtk-threads-enter/leave.  The pthreads has such
mutexes, but 1.6 would need extra code (unless it could be ommitted
there).

What does the gnome-gobject stuff do about thread protection?

At the moment I think I'll remove the offending bit from the manual
and worry later about something fancy in the code.