Keep interpolation on `replace`

[vitreo12]

Alga.boot;

(
a = AlgaNode({SinOsc.ar(\f.ar(330)).dup}, interpTime:2);
b = AlgaNode({DC.ar(200)});
o = AlgaNode({\in.ar(0).dup}, interpTime:1).play;
b >>.f a;
a >> o;
)

b.replace({DC.ar(400)})

a.it = 10

b.replace({DC.ar(1000)})

//trigger this while the interpolation is happening: it wouldn't work, 
//as the system is creating a whole new set of synths and patching them together
a.replace({Saw.ar(\f.ar(200) * 0.2)})

Here, when replacing a during the frequency interpolation, the interpolation is not maintained in the new node.

This will probably be unfixed.