Only remove wires that are assigned to constants.
This probably should run after ConstProp.

This means CSE need only be run once to get same QOR and prevents
pathological cases. Fixes #448

Fixes bug where arbitrary expressions, if called with .expr, return the
same expression.

Also add GlobalCircuitAnnotation for creating similar annotations

Now remove DefNodes of zero width
Don't deeply walk nodes (was the source of the bug)

Use newer rocket regression spec without comb loop

HTTPS clone is with .git; cd only with no error.