Taskjuggler: support the new effort durations

* lisp/org-taskjuggler.el (org-taskjuggler-clean-effort): handle any
effort that is accepted by `org-duration-string-to-minutes´.
* doc/org.texi (TaskJuggler export): Modified the example to reflect
the new effort durations.

The Effort property previously had no unit attached. With release 7.5
of orgmode you can now attach units to it such as 4h, 2d or 2m. This
patch enhances the exporter to accept the same effort specifications.

Note: This change is NOT BACKWARDS COMPATIBLE. Where the exporter
previously assumed a plain number was meant to be days, it now assumes
it to mean minutes. You will have to change existing effort
specifications from e.g. '2' to '2d'. A simple M-x
query-replace-regexp should do.

doc/org.texi

@@ -10674,15 +10674,15 @@ examples should illustrate this:
   :END:
 ** Markup Guidelines
    :PROPERTIES:
-   :Effort:   2.0
+   :Effort:   2d
    :END:
 ** Workflow Guidelines
    :PROPERTIES:
-   :Effort:   2.0
+   :Effort:   2d
    :END:
 * Presentation
   :PROPERTIES:
-  :Effort:   2.0
+  :Effort:   2d
   :BLOCKER:  training_material @{ gapduration 1d @} preparation
   :END:
 @end example

lisp/org-taskjuggler.el

@@ -126,15 +126,15 @@
 ;;   :END:
 ;; ** Markup Guidelines
 ;;    :PROPERTIES:
-;;    :Effort:   2.0
+;;    :Effort:   2d
 ;;    :END:
 ;; ** Workflow Guidelines
 ;;    :PROPERTIES:
-;;    :Effort:   2.0
+;;    :Effort:   2d
 ;;    :END:
 ;; * Presentation
 ;;   :PROPERTIES:
-;;   :Effort:   2.0
+;;   :Effort:   2d
 ;;   :BLOCKER:  training_material { gapduration 1d } some_other_task
 ;;   :END:
 ;;
@@ -613,20 +613,13 @@ is defined it will calculate a unique id for the resource using
 
 (defun org-taskjuggler-clean-effort (effort)
   "Translate effort strings into a format acceptable to taskjuggler,
-i.e. REAL UNIT. If the effort string is something like 5:30 it
-will be assumed to be hours and will be translated into 5.5h.
-Otherwise if it contains something like 3.0 it is assumed to be
-days and will be translated into 3.0d. Other formats that
-taskjuggler supports (like weeks, months and years) are currently
-not supported."
+i.e. REAL UNIT. A valid effort string can be anything that is
+accepted by `org-duration-string-to-minutes´."
   (cond
    ((null effort) effort)
-   ((string-match "\\([0-9]+\\):\\([0-9]+\\)" effort)
-    (let ((hours (string-to-number (match-string 1 effort)))
-	  (minutes (string-to-number (match-string 2 effort))))
-      (format "%dh" (+ hours (/ minutes 60.0)))))
-   ((string-match "\\([0-9]+\\).\\([0-9]+\\)" effort) (concat effort "d"))
-   (t (error "Not a valid effort (%s)" effort))))
+   (t (let* ((minutes (org-duration-string-to-minutes effort))
+	     (hours (/ minutes 60.0)))
+	(format "%.1fh" hours)))))
 
 (defun org-taskjuggler-get-priority (priority)
   "Return a priority between 1 and 1000 based on PRIORITY, an