Reduceron's garbage collection can loose the sharedness of references

[tommythorn]

This is the Lava dual of the emulator bug fixed in aadd78cf where the sharedness can be lost in copyChild.

What happens is that we see an already copied app and we use the stored forwarding pointer from the original reference, including the sharedness. This fails if the original reference was unique (which is allowed in heap Apps even though the App ends up shared), and the second visited reference was shared.

Quite subtle.