mark o-b-default-header-args:R as a safe local under proper conditions

* lisp/ob-R.el (org-babel-default-header-args:R): mark as a safe local
variable

lisp/ob-R.el

@@ -65,7 +65,20 @@
 			    (output value graphics))))
   "R-specific header arguments.")
 
+(defconst ob-R-safe-header-args
+  (append org-babel-safe-header-args
+	  '(:width :height :bg :units :pointsize :antialias :quality
+		   :compression :res :type :family :title :fonts
+		   :version :paper :encoding :pagecentre :colormodel
+		   :useDingbats :horizontal))
+  "Header args which are safe for R babel blocks.
+
+See `org-babel-safe-header-args' for documentation of the format of
+this variable.")
+
 (defvar org-babel-default-header-args:R '())
+(put 'org-babel-default-header-args:R 'safe-local-variable
+     (org-babel-header-args-safe-fn ob-R-safe-header-args))
 
 (defcustom org-babel-R-command "R --slave --no-save"
   "Name of command to use for executing R code."