How to spawn a thread within a GtkD button event handler

[Alaindevos]

No use geany. The error occurs also when no editor is open.
I think the gtk libraries are not meant to be used in 
multithreaded way, where gtk is not knowing what is happening.
A process in background doing file things is no problem.
It is when a process in background tries to update a lot of 
widgets.
Probably the internal event queue of gtk gets confused.