New option `org-clock-frame-title-format'.
* org-clock.el (org-frame-title-format-backup): New variable
to store the value of `frame-title-format' before `org-clock'
might replace it by `org-clock-frame-title-format'.
(org-clock-frame-title-format): New option.
(org-frame-title-string): Delete.
(org-clock-update-mode-line): Minor code reformatting.
(org-clock-in, org-clock-out, org-clock-cancel): Use
`org-clock-frame-title-format'.
See http://thread.gmane.org/gmane.emacs.orgmode/55477
Trying to update `frame-title-format' is tricky and error-prone, since
users can set up this variable in many different ways. AFAIK there is
no equivalent to `global-mode-string' for setting the frame title, we
would use it otherwise.
The user can still configure `org-clock-frame-title-format' the way he
wants.