Improved the VM's efficiency. The VM is as fast as the interpreter. :-(

Improved the VM's efficiency.  The VM is as fast as the interpreter.  :-(

* benchmark/lib.scm:  New file.
* benchmark/measure.scm:  New file.
* README:  Added useful pointers to various threads.
* doc/guile-vm.texi:  Fixed the description of `load-program' (it now expects
  _immediate_ integers).
* src/*.[ch]:  Use immediate integers whereever possible, as in the original
  code.  For `CONS', use `scm_cell' rather than `scm_cons'.

git-archimport-id: lcourtes@laas.fr--2004-libre/guile-vm--revival--0.6--patch-6