When building the process graph. Ardour usess
Route::direct_feeds_according_to_reality()
This function only tests if the current route (or any ioprocessors)
is feeding another route's *input*.
Inserts, Return and now Sidechains are ignored as destinations on the
destination route are not taken into account.
This is now resolved by adding an IOVector, a collection of all inputs
of the destination route.
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