How to use PROP_TYPE_BUTTON?

[Le phan Anh <phanl csse monash edu au>]

Hi all,

Have anyone got experience using this type when creating a PropDialog? I 
am using it to open up a new window ( I do my own things on that window 
and update the Dia object later on)

The hard thing is that just a copy of Dia object is passed to the event 
handler of PROP_TYPE_BUTTON, so the question is how to update the 
original one correctly

Thanks,