Add fortnight view to agenda

* doc/org.texi (Agenda commands): Document fortnight view.
* lisp/org-agenda.el (org-agenda-custom-commands-local-options):
(org-agenda-span): Add support for fortnight view.
(org-agenda-menu): Add fortnight view command.
(org-agenda-list):
(org-agenda-ndays-to-span): Add support for fortnight view.
(org-agenda-span-to-ndays): Add support for fortnight view.
(org-agenda-later): Add support for fortnight view.
(org-agenda-fortnight-view): New command.
(org-agenda-change-time-span): Add support for fortnight view.
(org-agenda-compute-starting-span): Add support for fortnight view.

This is a patch by Michael Gauland.

doc/org.texi

@@ -8642,6 +8642,7 @@ Delete other windows.
 @c
 @orgcmdkskc{v d,d,org-agenda-day-view}
 @xorgcmdkskc{v w,w,org-agenda-week-view}
+@xorgcmd{v t,org-agenda-fortnight-view}
 @xorgcmd{v m,org-agenda-month-view}
 @xorgcmd{v y,org-agenda-year-view}
 @xorgcmd{v SPC,org-agenda-reset-view}

lisp/org-agenda.el

@@ -330,6 +330,7 @@ the daily/weekly agenda, see `org-agenda-skip-function'.")
 			 (const org-agenda-span)
 			 (choice (const :tag "Day" 'day)
 				 (const :tag "Week" 'week)
+				 (const :tag "Fortnight" 'fortnight)
 				 (const :tag "Month" 'month)
 				 (const :tag "Year" 'year)
 				 (integer :tag "Custom")))
@@ -1138,6 +1139,7 @@ Custom commands can set this variable in the options section."
   :group 'org-agenda-daily/weekly
   :type '(choice (const :tag "Day" day)
 		 (const :tag "Week" week)
+		 (const :tag "Fortnight" fortnight)
 		 (const :tag "Month" month)
 		 (const :tag "Year" year)
 		 (integer :tag "Custom")))
@@ -2335,7 +2337,11 @@ The following commands are available:
      ["Week View" org-agenda-week-view
       :active (org-agenda-check-type nil 'agenda)
       :style radio :selected (eq org-agenda-current-span 'week)
-      :keys "v w  (or just w)"]
+      :keys "v w"]
+     ["Fortnight View" org-agenda-fortnight-view
+      :active (org-agenda-check-type nil 'agenda)
+      :style radio :selected (eq org-agenda-current-span 'fortnight)
+      :keys "v f"]
      ["Month View" org-agenda-month-view
       :active (org-agenda-check-type nil 'agenda)
       :style radio :selected (eq org-agenda-current-span 'month)
@@ -4172,7 +4178,7 @@ items if they have an hour specification like [h]h:mm."
 	   (sd (or start-day today))
 	   (ndays (org-agenda-span-to-ndays span sd))
 	   (org-agenda-start-on-weekday
-	    (if (eq ndays 7)
+	    (if (or (eq ndays 7) (eq ndays 14))
 		org-agenda-start-on-weekday))
 	   (thefiles (org-agenda-files nil 'ifmode))
 	   (files thefiles)
@@ -4341,6 +4347,7 @@ items if they have an hour specification like [h]h:mm."
   (cond ((symbolp n) n)
 	((= n 1) 'day)
 	((= n 7) 'week)
+	((= n 14) 'fortnight)
 	(t n)))
 
 (defun org-agenda-span-to-ndays (span &optional start-day)
@@ -4349,6 +4356,7 @@ START-DAY is an absolute time value."
   (cond ((numberp span) span)
 	((eq span 'day) 1)
 	((eq span 'week) 7)
+	((eq span 'fortnight) 14)
 	((eq span 'month)
 	 (let ((date (calendar-gregorian-from-absolute start-day)))
 	   (calendar-last-day-of-month (car date) (caddr date))))
@@ -7830,6 +7838,8 @@ With prefix ARG, go forward that many times the current span."
       (setq sd (+ arg sd)))
      ((eq span 'week)
       (setq sd (+ (* 7 arg) sd)))
+     ((eq span 'fortnight)
+      (setq sd (+ (* 14 arg) sd)))
      ((eq span 'month)
       (setq greg2 (list (+ (car greg) arg) (nth 1 greg) (nth 2 greg))
 	    sd (calendar-absolute-from-gregorian greg2))
@@ -7859,7 +7869,7 @@ With prefix ARG, go backward that many times the current span."
 (defun org-agenda-view-mode-dispatch ()
   "Call one of the view mode commands."
   (interactive)
-  (message "View: [d]ay        [w]eek       [m]onth       [y]ear   [SPC]reset  [q]uit/abort
+  (message "View: [d]ay  [w]eek  for[t]night  [m]onth  [y]ear  [SPC]reset  [q]uit/abort
       time[G]rid   [[]inactive  [f]ollow      [l]og    [L]og-all   [c]lockcheck
       [a]rch-trees [A]rch-files clock[R]eport include[D]iary       [E]ntryText")
   (let ((a (read-char-exclusive)))
@@ -7867,6 +7877,7 @@ With prefix ARG, go backward that many times the current span."
       (?\  (call-interactively 'org-agenda-reset-view))
       (?d (call-interactively 'org-agenda-day-view))
       (?w (call-interactively 'org-agenda-week-view))
+      (?t (call-interactively 'org-agenda-fortnight-view))
       (?m (call-interactively 'org-agenda-month-view))
       (?y (call-interactively 'org-agenda-year-view))
       (?l (call-interactively 'org-agenda-log-mode))
@@ -7905,6 +7916,15 @@ week 12 of year 2007.  Years in the range 1938-2037 can also be
 written as 2-digit years."
   (interactive "P")
   (org-agenda-change-time-span 'week iso-week))
+(defun org-agenda-fortnight-view (&optional iso-week)
+  "Switch to daily view for agenda.
+With argument ISO-WEEK, switch to the corresponding ISO week.
+If ISO-WEEK has more then 2 digits, only the last two encode the
+week.  Any digits before this encode a year.  So 200712 means
+week 12 of year 2007.  Years in the range 1938-2037 can also be
+written as 2-digit years."
+  (interactive "P")
+  (org-agenda-change-time-span 'fortnight iso-week))
 (defun org-agenda-month-view (&optional month)
   "Switch to monthly view for agenda.
 With argument MONTH, switch to that month."
@@ -7926,7 +7946,7 @@ written as 2-digit years."
 
 (defun org-agenda-change-time-span (span &optional n)
   "Change the agenda view to SPAN.
-SPAN may be `day', `week', `month', `year'."
+SPAN may be `day', `week', `fortnight', `month', `year'."
   (org-agenda-check-type t 'agenda)
   (let* ((args (get-text-property (min (1- (point-max)) (point)) 'org-last-args))
 	 (curspan (nth 2 args)))
@@ -7947,7 +7967,7 @@ SPAN may be `day', `week', `month', `year'."
 
 (defun org-agenda-compute-starting-span (sd span &optional n)
   "Compute starting date for agenda.
-SPAN may be `day', `week', `month', `year'.  The return value
+SPAN may be `day', `week', `fortnight', `month', `year'.  The return value
 is a cons cell with the starting date and the number of days,
 so that the date SD will be in that range."
   (let* ((greg (calendar-gregorian-from-absolute sd))
@@ -7960,7 +7980,7 @@ so that the date SD will be in that range."
 	(setq sd (+ (calendar-absolute-from-gregorian
 		     (list mg 1 yg))
 		    n -1))))
-     ((eq span 'week)
+     ((or (eq span 'week) (eq span 'fortnight))
       (let* ((nt (calendar-day-of-week
 		  (calendar-gregorian-from-absolute sd)))
 	     (d (if org-agenda-start-on-weekday