fixed some compilation warnings

* lisp/ob.el (org-number-sequence): declared
* lisp/ob-R.el (org-number-sequence): declared

lisp/ob-R.el

@@ -38,6 +38,7 @@
 (declare-function inferior-ess-send-input "ext:ess-inf" ())
 (declare-function ess-make-buffer-current "ext:ess-inf" ())
 (declare-function ess-eval-buffer "ext:ess-inf" (vis))
+(declare-function org-number-sequence "org-compat" (from &optional to inc))
 
 (defconst org-babel-header-arg-names:R
   '(width height bg units pointsize antialias quality compression

lisp/ob.el

@@ -72,6 +72,7 @@
 (declare-function org-babel-ref-resolve-reference "ob-ref"
 		  (ref &optional params))
 (declare-function org-babel-lob-execute-maybe "ob-lob" ())
+(declare-function org-number-sequence "org-compat" (from &optional to inc))
 
 (defgroup org-babel nil
   "Code block evaluation and management in `org-mode' documents."