1.0.1.15:
Add RESTART-FRAME command to the debugger, reduce the runtime cost
of the debug catch tags.
* Change the debugger catch tag to funcall the thrown value, rather
than just returning it.
* Make RETURN throw a thunk that returns an appropriate value,
and RESTART-FRAME throw a thunk that calls the same function again
with the same arguments.
* Always emit the debug catch with a static tag, rather than consing
up a new tag every time the catch is entered.
* To ensure that the tags are unique, the RETURN and RESTART-FRAME
commands will first cons up a new tag, find the right catch-block
structure on the stack, assign the new tag to the tag slot, and
then throw the new tag.
* Don't add the catch tags to some uninteresting (usually
compiler-generated) functions, to reduce the compilation speed
hit.