Implement new `U' mode switch for table formulas to omit seconds in durations

	* lisp/org-table.el (org-table-duration-custom-format): Add new
	HH:MM format.
	(org-table-duration-hour-zero-padding): New option.
	(org-table-eval-formula): Select second-less format if
	requested.
	(org-table-time-seconds-to-string): Implement formats without
	seconds and without zero-padding for hours.

	* testing/lisp/test-org-table.el (test-org-table/duration):
	New test for second-less durations.

	* doc/org.texi (Formula syntax for Calc)
	(Durations and time values): Document the U mode switch.

doc/org.texi

@@ -2664,7 +2664,7 @@ calculation precision is greater.
 Degree and radian angle modes of Calc.
 @item @code{F}, @code{S}
 Fraction and symbolic modes of Calc.
-@item @code{T}, @code{t}
+@item @code{T}, @code{t}, @code{U}
 Duration computations in Calc or Lisp, @pxref{Durations and time values}.
 @item @code{E}
 If and how to consider empty fields.  Without @samp{E} empty fields in range
@@ -2781,26 +2781,31 @@ Compute the sum of columns 1 to 4, like Calc's @code{vsum($1..$4)}.
 @cindex Time, computing
 @vindex org-table-duration-custom-format
 
-If you want to compute time values use the @code{T} flag, either in Calc
-formulas or Elisp formulas:
+If you want to compute time values use the @code{T}, @code{t}, or @code{U}
+flag, either in Calc formulas or Elisp formulas:
 
 @example
 @group
   |  Task 1 |   Task 2 |    Total |
   |---------+----------+----------|
   |    2:12 |     1:47 | 03:59:00 |
+  |    2:12 |     1:47 |    03:59 |
   | 3:02:20 | -2:07:00 |     0.92 |
-  #+TBLFM: @@2$3=$1+$2;T::@@3$3=$1+$2;t
+  #+TBLFM: @@2$3=$1+$2;T::@@3$3=$1+$2;U::@@4$3=$1+$2;t
 @end group
 @end example
 
 Input duration values must be of the form @code{HH:MM[:SS]}, where seconds
 are optional.  With the @code{T} flag, computed durations will be displayed
-as @code{HH:MM:SS} (see the first formula above).  With the @code{t} flag,
-computed durations will be displayed according to the value of the option
-@code{org-table-duration-custom-format}, which defaults to @code{'hours} and
-will display the result as a fraction of hours (see the second formula in the
-example above).
+as @code{HH:MM:SS} (see the first formula above).  With the @code{U} flag,
+seconds will be omitted so that the result will be only @code{HH:MM} (see
+second formula above).  Zero-padding of the hours field will depend upon the
+value of the variable @code{org-table-duration-hour-zero-padding}.
+
+With the @code{t} flag, computed durations will be displayed according to the
+value of the option @code{org-table-duration-custom-format}, which defaults
+to @code{'hours} and will display the result as a fraction of hours (see the
+third formula in the example above).
 
 Negative duration values can be manipulated as well, and integers will be
 considered as seconds in addition and subtraction.

lisp/org-table.el

@@ -294,13 +294,23 @@ relies on the variables to be present in the list."
 The default value is `hours', and will output the results as a
 number of hours.  Other allowed values are `seconds', `minutes' and
 `days', and the output will be a fraction of seconds, minutes or
-days."
+days. `hh:mm' selects to use hours and minutes, ignoring seconds.
+The `U' flag in a table formula will select this specific format for
+a single formula."
   :group 'org-table-calculation
   :version "24.1"
   :type '(choice (symbol :tag "Seconds" 'seconds)
 		 (symbol :tag "Minutes" 'minutes)
 		 (symbol :tag "Hours  " 'hours)
-		 (symbol :tag "Days   " 'days)))
+		 (symbol :tag "Days   " 'days)
+		 (symbol :tag "HH:MM  " 'hh:mm)))
+
+(defcustom org-table-duration-hour-zero-padding t
+  "Non-nil means, hours in table duration computations should be zero-padded.
+So this is about 08:32:34 versus 8:33:34."
+  :group 'org-table-calculation
+  :version "24.1"
+  :type 'boolean)
 
 (defcustom org-table-formula-field-format "%s"
   "Format for fields which contain the result of a formula.
@@ -2723,15 +2733,14 @@ location of point."
 					     (?s . sci) (?e . eng))))
 			     n))))
 	      (setq fmt (replace-match "" t t fmt)))
-	    (if (string-match "T" fmt)
-		(setq duration t numbers t
-		      duration-output-format nil
-		      fmt (replace-match "" t t fmt)))
-	    (if (string-match "t" fmt)
-		(setq duration t
-		      duration-output-format org-table-duration-custom-format
-		      numbers t
-		      fmt (replace-match "" t t fmt)))
+	    (if (string-match "[tTU]" fmt)
+		(let ((ff (match-string 0 fmt)))
+		  (setq duration t numbers t
+			duration-output-format
+			(cond ((equal ff "T") nil)
+			      ((equal ff "t") org-table-duration-custom-format)
+			      ((equal ff "U") 'hh:mm))
+			fmt (replace-match "" t t fmt))))
 	    (if (string-match "N" fmt)
 		(setq numbers t
 		      fmt (replace-match "" t t fmt)))
@@ -3759,7 +3768,17 @@ minutes or seconds."
 		 (format "%.1f" (/ (float secs0) 60)))
 		((eq output-format 'seconds)
 		 (format "%d" secs0))
-		(t (format-seconds "%.2h:%.2m:%.2s" secs0)))))
+		((eq output-format 'hh:mm)
+		 ;; Ignore seconds
+		 (substring (format-seconds
+			     (if org-table-duration-hour-zero-padding
+				 "%.2h:%.2m:%.2s" "%h:%.2m:%.2s")
+			     secs0)
+			    0 -3))
+		(t (format-seconds
+		    (if org-table-duration-hour-zero-padding
+			"%.2h:%.2m:%.2s" "%h:%.2m:%.2s")
+		    secs0)))))
     (if (< secs 0) (concat "-" res) res)))
 
 (defun org-table-fedit-convert-buffer (function)

testing/lisp/test-org-table.el

@@ -1809,6 +1809,13 @@ is t, then new columns should be added as needed"
        <point>#+TBLFM: @1$3=$1+$2;T"
 		   (org-table-calc-current-TBLFM)
 		   (buffer-string))))
+  (should
+   (string-match "| 2:12 | 1:47 | 03:59 |"
+		 (org-test-with-temp-text "
+       | 2:12 | 1:47 | |
+       <point>#+TBLFM: @1$3=$1+$2;U"
+		   (org-table-calc-current-TBLFM)
+		   (buffer-string))))
   (should
    (string-match "| 3:02:20 | -2:07:00 | 0.92 |"
 		 (org-test-with-temp-text "