Improve XEmacs compatibility
* lisp/org-compat.el (org-number-sequence): New function.
* lisp/ob-R.el (org-babel-expand-body:R): Use `org-number-sequence'.
* lisp/ob.el (org-babel-where-is-src-block-result): Use `org-number-sequence'.
(org-babel-current-buffer-properties): Fix variable definition.
* lisp/ob-ref.el (org-babel-ref-index-list): Use `org-number-sequence'.
* lisp/ob-latex.el (org-babel-latex-tex-to-pdf): Use the 2-argument version
of `shell-command'.
* lisp/org-latex.el (org-export-as-pdf): Use the 2-argument version
of `shell-command'.