* Compiler now knows how to emit a different form of

* Compiler now knows how to emit a different form of
`dbg-info-vector', which contains not only the compiled-code blocks
(as before), but also a pointer which is the root to be used if the
code is to be purified.  The runtime system needed to be changed to
accomodate this.

* Change default for `load-debugging-info-on-demand?' back to false.

* Fix `scode-constant?' to handle compiled-code-entry objects
correctly.