org: forward declare functions

* lisp/org.el: Forward declare `org-clock-sum',
  `org-table-end-of-field', `org-element-cache-refresh'.

These have been introduced with b5554077cb, b76071f2b6 and 6eb940a8dc.

lisp/org.el

@@ -130,6 +130,7 @@ Stars are put in group 1 and the trimmed body in group 2.")
 (declare-function org-clock-timestamps-up "org-clock" (&optional n))
 (declare-function org-clock-timestamps-down "org-clock" (&optional n))
 (declare-function org-clock-remove-overlays "org-clock" (&optional beg end noremove))
+(declare-function org-clock-sum "org-clock" (&optional tstart tend headline-filter propname))
 (declare-function org-clock-sum-current-item "org-clock" (&optional tstart))
 (declare-function org-clock-update-time-maybe "org-clock" ())
 (declare-function org-clocktable-shift "org-clock" (dir n))
@@ -155,6 +156,7 @@ Stars are put in group 1 and the trimmed body in group 2.")
 (declare-function org-table-begin "org-table" (&optional table-type))
 (declare-function org-table-blank-field "org-table" ())
 (declare-function org-table-end "org-table" (&optional table-type))
+(declare-function org-table-end-of-field "org-table" (&optional n))
 (declare-function org-table-insert-row "org-table" (&optional arg))
 (declare-function org-table-paste-rectangle "org-table" ())
 (declare-function org-table-maybe-eval-formula "org-table" ())
@@ -164,6 +166,7 @@ Stars are put in group 1 and the trimmed body in group 2.")
 		  (beg end acc restriction))
 (declare-function org-element-at-point "org-element" ())
 (declare-function org-element-cache-reset "org-element" (&optional all))
+(declare-function org-element-cache-refresh "org-element" (pos))
 (declare-function org-element-contents "org-element" (element))
 (declare-function org-element-context "org-element" (&optional element))
 (declare-function org-element-interpret-data "org-element"