Detect scrollbar change due to user interaction

[Kasper Peeters <kasper peeters phi-sci com>]

I want to detect whether a scrollbar has moved due to a user
interaction (dragging the slider, clicking up/down arrows, rolling the
scroll wheel). The signal_value_changed also fires on scrollbar
changes due to e.g. the content of the associated ScrolledWindow
changing, and I don't want to know about such (programmatic) changes.
Any suggestions, or a pointer to the preferred way to do this?

Thanks,
Kasper