Need control of filename entry area in gtkfilechooser

[Ferdinand Ramirez <ramirez ferdinand yahoo com>]

When I type in the filename into the filename entry area in gtkfilechooser dialog, I want to intercept the 
text that is entered, modify it and then display it in the filename area. How do I do this?

For a regular text buffer, I know how to do this: I can do a gtk_text_view_get_buffer and then have a 
callback for insert-text. I can then modify the text that is entered and then insert it into the buffer, all 
from inside the callback.

I want to be able to achieve the same thing for filename entry. Does anyone know how to do this?

Thanks,
-Ferdinand