Emitter: Boxing of call variants now works on trees, moves to values.
Emitter: Boxing of call variants now works on trees, moves to values.

In the future, partially-evaluated variants won't be pushing values.
Therefore, reboxing of variant values needs to not depend on a value
being pushed, but on what the tree wrote and fixing that up. So this
is a nice little step toward better variants.

FascinatedBox/lily,FascinatedBox/lily,jesserayadkins/lily,FascinatedBox/lily,jesserayadkins/lily,jesserayadkins/lily,FascinatedBox/lily