Getting new computable design working.

Computed values are now themselves, not wrappers around values.
If they are atomic, then they are Object()'ized.
This required minor changes to U (upwardable) as well.

All the logic for capturing dependencies, observing dependencies,
recomputing, and having upwardables watch their members for
computable-related changes, now seem to work more or less.

Next step is more individual case testing, then writing those tests
using the testing framework. Next we'll tackle rewriting things like
map, which have been broken for a long time, but should be quite simple
using the new framework. ALl the other methods such as slice or filter
should also be thrown away and rewritten, hopefully now in a few lines.