cancelling a drag from a widget

[Elliott Hughes <Elliott Hughes genedata com>]

i've written a widget where, if the user uses gtk_drag_source_set,
i only want a drag to start from certain `active' areas within the
widget. how can i do this? basically, i want to check the x and
y start coordinates of the drag from within drag_start, and tell
gtk not to initiate a drag if it doesn't make sense from that part
of the component.

i can get the relevant x and y coordinates from the button_press
that comes before drag_start, but what i don't know how to do is
prevent the drag. certainly, it seems that calling gtk_drag_finish
from within drag_start causes trouble.

does this need drag_start to return gboolean, and have the code
in gtkdnd.c check whether or not to continue, or is it possible in
the system as it stands?

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