bug#21162: adapting octave-inf.el to Octave 4

[Francesco Potortì]

The following patch does two things:

1) it removes the --no-line-editing option when calling the Octave
   process, for reasons that I explained in my previous bug report about
   octave-inf.el

2) it adds the --no-gui option when calling Octave if its version is
   different from 3: this is needed because the last (and future,
   probably) Octave versions launch a GUI by default

--- /dev/fd/63  2015-07-30 19:21:16.227231663 +0200
+++ octave-inf.el       2015-07-30 19:13:13.678557317 +0200
@@ -193,12 +193,16 @@
 
 (defun inferior-octave-startup ()
   "Start an inferior Octave process."
-  (let ((proc (comint-exec-1
-              (substring inferior-octave-buffer 1 -1)
-              inferior-octave-buffer
-              inferior-octave-program
-              (append (list "-i" "--no-line-editing")
-                      inferior-octave-startup-args))))
+  (let* ((octave-version-string (shell-command-to-string
+                                (concat inferior-octave-program " --version")))
+        (octave-gui (not (string-match "version 3" octave-version-string)))
+        (proc (comint-exec-1
+               (substring inferior-octave-buffer 1 -1)
+               inferior-octave-buffer
+               inferior-octave-program
+               (append (list "-i")
+                       (when octave-gui (list "--no-gui"))
+                       inferior-octave-startup-args))))
     (set-process-filter proc 'inferior-octave-output-digest)
     (setq comint-ptyp process-connection-type
          inferior-octave-process proc