Refactorize helm-open-file-externally and friends.

* helm-external.el (helm-get-default-program-for-file): Do it.
(helm-open-file-externally):                            Do it.

helm-external.el

@@ -131,56 +131,53 @@ Try first in `helm-external-programs-associations' and then in mailcap file
 if nothing found return nil."
   (let* ((ext      (file-name-extension filename))
          (def-prog (assoc-default ext helm-external-programs-associations)))
-    (cond ((and def-prog (not (string= def-prog "")))
-           (concat def-prog " %s"))
-          ((and helm-default-external-file-browser
-                (file-directory-p filename))
-           (concat helm-default-external-file-browser " %s"))
+    (cond ((and def-prog (not (string= def-prog ""))) def-prog)
+          ((and helm-default-external-file-browser (file-directory-p filename))
+           helm-default-external-file-browser)
           (t (helm-get-mailcap-for-file filename)))))
 
 (defun helm-open-file-externally (file)
   "Open FILE with an external program.
 Try to guess which program to use with `helm-get-default-program-for-file'.
 If not found or a prefix arg is given query the user which tool to use."
-  (let* ((fname          (expand-file-name file))
-         (collection     (helm-external-commands-list-1 'sort))
-         (def-prog       (helm-get-default-program-for-file fname))
-         (real-prog-name (if (or helm-current-prefix-arg (not def-prog))
-                             ;; Prefix arg or no default program.
-                             (prog1
-                                 (helm-comp-read
-                                  "Program: " collection
-                                  :must-match t
-                                  :name "Open file Externally"
-                                  :del-input nil
-                                  :history helm-external-command-history)
-                               ;; Always prompt to set this program as default.
-                               (setq def-prog nil))
-                           ;; No prefix arg or default program exists.
-                           (replace-regexp-in-string " %s\\| '%s'" "" def-prog)))
-         (program        (concat real-prog-name " %s")))
+  (let* ((fname      (expand-file-name file))
+         (collection (helm-external-commands-list-1 'sort))
+         (def-prog   (helm-get-default-program-for-file fname))
+         (program    (if (or helm-current-prefix-arg (not def-prog))
+                         ;; Prefix arg or no default program.
+                         (prog1
+                             (helm-comp-read
+                              "Program: " collection
+                              :must-match t
+                              :name "Open file Externally"
+                              :del-input nil
+                              :history helm-external-command-history)
+                           ;; Always prompt to set this program as default.
+                           (setq def-prog nil))
+                         ;; No prefix arg or default program exists.
+                         def-prog)))
     (unless (or def-prog ; Association exists, no need to record it.
                 ;; Don't try to record non--filenames associations (e.g urls).
                 (not (file-exists-p fname)))
       (when
           (y-or-n-p
            (format
             "Do you want to make `%s' the default program for this kind of files? "
-            real-prog-name))
+            program))
         (helm-aif (assoc (file-name-extension fname)
                          helm-external-programs-associations)
             (setq helm-external-programs-associations
                   (delete it helm-external-programs-associations)))
         (push (cons (file-name-extension fname)
                     (helm-read-string
-                     "Program (Add args maybe and confirm): " real-prog-name))
+                     "Program (Add args maybe and confirm): " program))
               helm-external-programs-associations)
         (customize-save-variable 'helm-external-programs-associations
                                  helm-external-programs-associations)))
     (helm-run-or-raise program file)
     (setq helm-external-command-history
-          (cons real-prog-name
-                (delete real-prog-name
+          (cons program
+                (delete program
                         (cl-loop for i in helm-external-command-history
                               when (executable-find i) collect i))))))