org-babel: Fix usage of `org-babel-temporary-directory'

* lisp/ob-core.el (org-babel-temp-directory): New macro, returning
suitable temporary directory.  The macro considers remote
`default-directory' and nil values of
`org-babel-temporary-directory'.
* lisp/ob-gnuplot.el (org-babel-gnuplot-process-vars):
* lisp/ob-java.el (org-babel-execute:java):
* lisp/ob-processing.el (org-babel-processing-view-sketch): Use the
new macro.

Reported-by: Christian Köstlin <christian.koestlin@gmail.com>

lisp/ob-core.el

@@ -3273,6 +3273,15 @@ Emacs shutdown.")
 	   ,scalar-form
 	 ,@table-forms))))
 
+(defmacro org-babel-temp-directory ()
+  "Return temporary directory suitable for `default-directory'."
+  `(if (file-remote-p default-directory)
+       org-babel-remote-temporary-directory
+     (or (and org-babel-temporary-directory
+	      (file-exists-p org-babel-temporary-directory)
+	      org-babel-temporary-directory)
+	 temporary-file-directory)))
+
 (defun org-babel-temp-file (prefix &optional suffix)
   "Create a temporary file in the `org-babel-temporary-directory'.
 Passes PREFIX and SUFFIX directly to `make-temp-file' with the

lisp/ob-gnuplot.el

@@ -106,7 +106,7 @@ code."
 		     (file-remote-p val)  ;; check if val is a remote file
 		     (file-exists-p val)) ;; call to file-exists-p is slow, maybe remove it
 		(let* ((local-name (concat ;; create a unique filename to avoid multiple downloads
-				    org-babel-temporary-directory
+				    (org-babel-temp-directory)
 				    "/gnuplot/"
 				    (file-remote-p val 'host)
 				    (org-babel-local-file-name val))))

lisp/ob-java.el

@@ -193,7 +193,7 @@ replaced in this string.")
                                                   (concat
                                                    (file-remote-p default-directory)
                                                    org-babel-remote-temporary-directory)
-                                                org-babel-temporary-directory)
+                                                (org-babel-temp-directory))
                                             default-directory)))
          ;; the dir to write the source file
          (packagedir (if (and (not run-from-temp) packagename)

lisp/ob-processing.el

@@ -93,7 +93,7 @@
 	  ;; make-temp-file is repeated until no hyphen is in the
 	  ;; name; also sketch dir name must be the same as the
 	  ;; basename of the sketch file.
-	  (let* ((temporary-file-directory org-babel-temporary-directory)
+	  (let* ((temporary-file-directory (org-babel-temp-directory))
 		 (sketch-dir
 		  (let (sketch-dir-candidate)
 		    (while