bugfix: fix `org-babel-execute-src-block' on remote hosts

* lisp/ob-core.el (org-babel-temp-file): For remote hosts, modify the prefix
  and leave `temporary-file-directory' unchanged.

The reason setting `temporary-file-directory' doesn't work here is
because `make-temp-file' recursively calls itself (indirectly).
Modifying `temporary-file-directly', affects the recursive calls as well,
which results in a "No such file file or directory" error.

The fix is to leave `temporary-file-directory' unaltered, for remote
hosts, and instead modifying the 'prefix' argument to `make-temp-file'
appropriately.

TINYCHANGE

lisp/ob-core.el

@@ -2641,14 +2641,17 @@ Emacs shutdown."))
 Passes PREFIX and SUFFIX directly to `make-temp-file' with the
 value of `temporary-file-directory' temporarily set to the value
 of `org-babel-temporary-directory'."
-  (let ((temporary-file-directory
-	 (if (file-remote-p default-directory)
-	     (concat (file-remote-p default-directory) "/tmp")
+  (if (file-remote-p default-directory)
+      (let ((prefix
+             (concat (file-remote-p default-directory)
+                     (expand-file-name prefix temporary-file-directory))))
+        (make-temp-file prefix nil suffix))
+    (let ((temporary-file-directory
 	   (or (and (boundp 'org-babel-temporary-directory)
 		    (file-exists-p org-babel-temporary-directory)
 		    org-babel-temporary-directory)
-	       temporary-file-directory))))
-      (make-temp-file prefix nil suffix)))
+	       temporary-file-directory)))
+      (make-temp-file prefix nil suffix))))
 
 (defun org-babel-remove-temporary-directory ()
   "Remove `org-babel-temporary-directory' on Emacs shutdown."