Eliminating duplicated code (take 2...).

Eliminating duplicated code (take 2...).

This proposal for code tidying uses multiple-value-bind to satisfy:

1. The various parsed/resolved components of the param list (session,
   vars, result-type) are available in the org-babel-execute:LANG
   functions.
2. Those functions don't duplicate the code for parsing the params
   list and resolving references
3. The functions still have the params list available to them, should
   they need to implement language-specific behaviour using it.

If the org-babel-execute:LANG functions need to be called directly,
then that would now have to be via
(multiple-value-bind (session vars result-params result-type)
      (org-babel-process-params params) (funcall cmd body params))

as in org-babel-exp.el. (But is it actually necessary to by-pass
org-babel-execute-src-block?)