improved gnuplot handling of special header args

  Both declare them, and then actually retrieve them from the params
  association list (which is not a p list).

* lisp/ob-gnuplot.el (org-babel-header-args:gnuplot): Declare them.
  (org-babel-expand-body:gnuplot): Params is an alist not a plist.

lisp/ob-gnuplot.el

@@ -53,7 +53,14 @@
   "Default arguments to use when evaluating a gnuplot source block.")
 
 (defvar org-babel-header-args:gnuplot
-  '((missing . :any))
+  '((title	. :any)
+    (lines	. :any)
+    (sets	. :any)
+    (x-labels	. :any)
+    (y-labels	. :any)
+    (timefmt	. :any)
+    (time-ind	. :any)
+    (missing	. :any))
   "Gnuplot specific header args.")
 
 (defvar org-babel-gnuplot-timestamp-fmt nil)
@@ -84,13 +91,13 @@ code."
            (term (or (cdr (assoc :term params))
                      (when out-file (file-name-extension out-file))))
            (cmdline (cdr (assoc :cmdline params)))
-           (title (plist-get params :title))
-           (lines (plist-get params :line))
-           (sets (plist-get params :set))
-           (x-labels (plist-get params :xlabels))
-           (y-labels (plist-get params :ylabels))
-           (timefmt (plist-get params :timefmt))
-           (time-ind (or (plist-get params :timeind)
+           (title (cdr (assoc :title params)))
+           (lines (cdr (assoc :line params)))
+           (sets (cdr (assoc :set params)))
+           (x-labels (cdr (assoc :xlabels params)))
+           (y-labels (cdr (assoc :ylabels params)))
+           (timefmt (cdr (assoc :timefmt params)))
+           (time-ind (or (cdr (assoc :timeind params))
                          (when timefmt 1)))
 	   (missing (cdr (assoc :missing params)))
 	   (add-to-body (lambda (text) (setq body (concat text "\n" body))))