Ensure backwards compatibility for all users

We check whether eval-and-grab-output caller presumes older interface
to it and return a legacy list of two elements instead of alist in
those cases.

It is certainly appropriate to drop this check when Emacs 27 becomes
history. It is very likely appropriate to drop when use of Org 9.4
becomes discouraged by Org developers.

swank.lisp

@@ -1762,7 +1762,8 @@ Errors are trapped and invoke our debugger."
         (format-values-for-echo-area values)))))
 
 (defslimefun eval-and-grab-output
-    (string &optional (targets-to-capture '(*standard-output* values)))
+    (string &optional (targets-to-capture '(*standard-output* values)
+                                          targets-provided-p))
   "Evaluate contents of STRING, return alist of results including various output streams. Possible keys in the returned alist should be listed in the value of `slime-output-targets' variable in `slime.el'."
   (with-buffer-syntax ()
     (with-retry-restart (:msg "Retry SLIME evaluation request.")
@@ -1785,16 +1786,27 @@ Errors are trapped and invoke our debugger."
                (*standard-output*
                  (maybe-make-string-output-stream *standard-output*))
                (values (multiple-value-list (eval (from-string string)))))
-          ;; It is not clear what would be the most natural order here.
-          ;; We picked the reversed binding order.
-          (list (cons 'values
-                      (maybe-value-string (format nil "~{~S~^~%~}" values))) 
-                (cons '*standard-output*
-                      (maybe-output-stream-string *standard-output*))
-                (cons '*error-output*
-                      (maybe-output-stream-string *error-output*))
-                (cons '*trace-output*
-                      (maybe-output-stream-string *trace-output*))))))))
+          (if targets-provided-p
+              ;; It is not clear what would be the most natural order here.
+              ;; We picked the reversed binding order.
+              (list
+               (cons 'values
+                     (maybe-value-string (format nil "~{~S~^~%~}" values)))
+               (cons '*standard-output*
+                     (maybe-output-stream-string *standard-output*))
+               (cons '*error-output*
+                     (maybe-output-stream-string *error-output*))
+               (cons '*trace-output*
+                     (maybe-output-stream-string *trace-output*)))
+              ;; targets are not provided by callers
+              ;; who presume older (pre-2.26) interface
+              ;; to eval-and-grab-output
+              ;; This check (and targets-provided-p argument itself)
+              ;; - can certainly be dropped when Emacs 27 becomes unsupported
+              ;; - can very likely be dropped when Org 9.4 becomes unsupported
+              (list (maybe-output-stream-string *standard-output*)
+                    (maybe-value-string
+                     (format nil "~{~S~^~%~}" values)))))))))
 
 (defun eval-region (string)
   "Evaluate STRING.