New option to format the total time cells.

* org-clock.el (org-clock-in-prepare-hook): New option to
format the total time cells.
(org-clocktable-write-default): Use the new option.

lisp/org-clock.el

@@ -323,6 +323,12 @@ play with them."
   :version "24.1"
   :type 'boolean)
 
+(defcustom org-clock-total-time-cell-format "*%s*"
+  "Format string for the total time cells."
+  :group 'org-clock
+  :version "24.1"
+  :type 'boolean)
+
 (defvar org-clock-in-prepare-hook nil
   "Hook run when preparing the clock.
 This hook is run before anything happens to the task that
@@ -2231,11 +2237,11 @@ from the dynamic block definition."
 				         ; file column, maybe
        (if level-p   "|"      "")        ; level column, maybe
        (if timestamp "|"      "")        ; timestamp column, maybe
-       (if properties (make-string (length properties) ?|) "")  ;properties columns, maybe
-       (concat "*" (nth 7 lwords) "*| ") ; instead of a headline
-       "*"
-       (org-minutes-to-hh:mm-string (or total-time 0)) ; the time
-       "*|\n")                          ; close line
+       (if properties (make-string (length properties) ?|) "")  ; properties columns, maybe
+       (concat (format org-clock-total-time-cell-format (nth 7 lwords))  "| ") ; instead of a headline
+       (format org-clock-total-time-cell-format
+	       (org-minutes-to-hh:mm-string (or total-time 0))) ; the time
+       "|\n")                          ; close line
 
       ;; Now iterate over the tables and insert the data
       ;; but only if any time has been collected