smp: Clobber fluid-let and the (runtime state-space) package.

smp: Clobber fluid-let and the (runtime state-space) package.

UNimplement fluid-let using dynamic-wind as a backward compatibility
kludge.  Subsystems still using fluid-let, e.g. LIAR, must not be run
in multiple threads simultaneously.  Fluid-let no longer provides
thread-local storage.

Replace the previously fluid-assigned bindings state-space:local and
(runtime dynamic)bindings with thread slots dynamic-point and
dynamic-environment.  Split the initialization of (runtime thread)
into "low" and "high" procedures.  The "low" procedure is applied
early in the bootstrap to create the initial thread, whose dynamic
state is needed later.  Lose the error handling in wait-for-io; it
runs when there is no current thread, thus no way to bind-condition-
handler.

Replace the uniprocessor-only Hanson/Lamping state-spaces with
Scheme48's multiprocessing-friendly dynamic-points in a new package
(runtime wind).