Document what a variant 12 means in the serialization format.
Simplify conversion from sign-manitude to two's complement in nqp_bigint_shr()
Fix spurious "too late to set encoding" errors.
Handle a bunch of the derived properties.
The rest we need for properties-derived.t.
Unify shift ops. Shifting by negative amounts flips direction.
Start stubbing in BootJavaInterop
GlobalContext.getCurrentThreadContext
Sanity check in serialization writer.
Another sanity check in repossession.