Toothbrush: Added save-exec feature; cleaned up warnings for SBCL.

The save-exec feature is tested in
books/system/toothbrush/tests/test1/; see the Makefile there.

Note: Gary Byers has written code to shrink the image somewhat created
by save-exec, though not a great deal.  I plan to incorporate it when
I know what copyright/license to use.