ob-core: Make `org-babel-hash-show-time' a defcustom

* lisp/ob-core.el (org-babel-hash-show-time): Change into a defcustom.

etc/ORG-NEWS

@@ -526,6 +526,9 @@ indication letter was solely J.
 When ~org-special-ctrl-o~ is non-nil, it is impractical to create
 a blank line above a table at the beginning of the document. Now, as
 a special case, ~org-open-line~ behaves normally in this situation.
+*** ~org-babel-hash-show-time~ is now customizable
+The experimental variable used to be more less confidential, as
+a ~defvar~.
 * Version 8.3
 
 ** Incompatible changes

lisp/ob-core.el

@@ -171,6 +171,14 @@ This string must include a \"%s\" which will be replaced by the results."
        (and (stringp value)
 	    (string-match-p "%s" value))))
 
+(defcustom org-babel-hash-show-time nil
+  "Non-nil means show the time the code block was evaluated in the result hash."
+  :group 'org-babel
+  :type 'boolean
+  :version "25.2"
+  :package-version '(Org . "9.0")
+  :safe #'booleanp)
+
 (defun org-babel-noweb-wrap (&optional regexp)
   (concat org-babel-noweb-wrap-start
 	  (or regexp "\\([^ \t\n].+?[^ \t]\\|[^ \t\n]\\)")
@@ -518,9 +526,6 @@ to raise errors for all languages.")
 (defvar org-babel-hash-show 4
   "Number of initial characters to show of a hidden results hash.")
 
-(defvar org-babel-hash-show-time nil
-  "Non-nil means show the time the code block was evaluated in the result hash.")
-
 (defvar org-babel-after-execute-hook nil
   "Hook for functions to be called after `org-babel-execute-src-block'")