S-M-<up/down> now adjusts previous/next clock when hit on clock timestamps.

S-M-<up/down> now adjusts previous/next clock when hit on clock timestamps.

* org.el (org-clock-history, org-clock-adjust-closest): New
variables.
(org-timestamp-change): Maybe adjust the next or previous
clock in `org-clock-history'.
(org-shiftmetaup, org-shiftmetadown): On clock logs, update
the timestamp at point and adjust the next or previous clock
in `org-clock-history', when possible.

* org.texi (Clocking commands): Document the use of
S-M-<up/down> on clock timestamps.

Thanks to Joseph Thomas who suggested this.